Python3.8.5にてPillowパッケージをインストールできません

前提・実現したいこと

PythonでPillowというライブラリをインストールしたいです。

発生している問題・エラーメッセージ

pipコマンドにてPillowをインストールしようとしても下記エラーが出ます。

PS C:\Users\username> pip install Pillow
WARNING: Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProtocolError('Connection aborted.', FileNotFoundError(2, 'No such file or directory'))': /simple/pillow/
WARNING: Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProtocolError('Connection aborted.', FileNotFoundError(2, 'No such file or directory'))': /simple/pillow/
WARNING: Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProtocolError('Connection aborted.', FileNotFoundError(2, 'No such file or directory'))': /simple/pillow/
WARNING: Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProtocolError('Connection aborted.', FileNotFoundError(2, 'No such file or directory'))': /simple/pillow/
WARNING: Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ProtocolError('Connection aborted.', FileNotFoundError(2, 'No such file or directory'))': /simple/pillow/
ERROR: Could not find a version that satisfies the requirement Pillow
ERROR: No matching distribution found for Pillow

試したこと

下記コマンドを実行

python3 -m pip install --upgrade pip
python3 -m pip install --upgrade Pillow

同じエラーが出ます。

管理者権限にてCMD実行

同じエラーが出ます。

-vをつけて実行

C:\WINDOWS\system32>pip install -v Pillow
Using pip 21.0.1 from c:\python38\lib\site-packages\pip (python 3.8)
Non-user install because site-packages writeable
Created temporary directory: C:\Users\username\AppData\Local\Temp\pip-ephem-wheel-cache-hks29fcu
Created temporary directory: C:\Users\username\AppData\Local\Temp\pip-req-tracker-7c3v3app
Initialized build tracking at C:\Users\username\AppData\Local\Temp\pip-req-tracker-7c3v3app
Created build tracker: C:\Users\username\AppData\Local\Temp\pip-req-tracker-7c3v3app
Entered build tracker: C:\Users\username\AppData\Local\Temp\pip-req-tracker-7c3v3app
Created temporary directory: C:\Users\username\AppData\Local\Temp\pip-install-d39skl80
1 location(s) to search for versions of pillow:
* https://pypi.org/simple/pillow/
Fetching project page and analyzing links: https://pypi.org/simple/pillow/
Getting page https://pypi.org/simple/pillow/
Found index url https://pypi.org/simple
Looking up "https://pypi.org/simple/pillow/" in the cache
Request header has "max_age" as 0, cache bypassed
Starting new HTTPS connection (1): pypi.org:443
Incremented Retry for (url='/simple/pillow/'): Retry(total=4, connect=None, read=None, redirect=None, status=None)
Starting new HTTPS connection (2): pypi.org:443
Incremented Retry for (url='/simple/pillow/'): Retry(total=3, connect=None, read=None, redirect=None, status=None)
Starting new HTTPS connection (3): pypi.org:443
Incremented Retry for (url='/simple/pillow/'): Retry(total=2, connect=None, read=None, redirect=None, status=None)
Starting new HTTPS connection (4): pypi.org:443
Incremented Retry for (url='/simple/pillow/'): Retry(total=1, connect=None, read=None, redirect=None, status=None)
Starting new HTTPS connection (5): pypi.org:443
Incremented Retry for (url='/simple/pillow/'): Retry(total=0, connect=None, read=None, redirect=None, status=None)
Starting new HTTPS connection (6): pypi.org:443
Could not fetch URL https://pypi.org/simple/pillow/: connection error: HTTPSConnectionPool(host='pypi.org', port=443): Max retries exceeded with url: /simple/pillow/ (Caused by ProtocolError('Connection aborted.', FileNotFoundError(2, 'No such file or directory'))) - skipping
Given no hashes to check 0 links for project 'pillow': discarding no candidates
Exception information:
Traceback (most recent call last):
  File "c:\python38\lib\site-packages\pip\_vendor\resolvelib\resolvers.py", line 171, in _merge_into_criterion
    crit = self.state.criteria[name]
KeyError: 'pillow'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "c:\python38\lib\site-packages\pip\_vendor\resolvelib\resolvers.py", line 318, in resolve
    name, crit = self._merge_into_criterion(r, parent=None)
  File "c:\python38\lib\site-packages\pip\_vendor\resolvelib\resolvers.py", line 173, in _merge_into_criterion
    crit = Criterion.from_requirement(self._p, requirement, parent)
  File "c:\python38\lib\site-packages\pip\_vendor\resolvelib\resolvers.py", line 83, in from_requirement
    raise RequirementsConflicted(criterion)
pip._vendor.resolvelib.resolvers.RequirementsConflicted: Requirements conflict: SpecifierRequirement('Pillow')

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "c:\python38\lib\site-packages\pip\_internal\resolution\resolvelib\resolver.py", line 121, in resolve
    self._result = resolver.resolve(
  File "c:\python38\lib\site-packages\pip\_vendor\resolvelib\resolvers.py", line 453, in resolve
    state = resolution.resolve(requirements, max_rounds=max_rounds)
  File "c:\python38\lib\site-packages\pip\_vendor\resolvelib\resolvers.py", line 320, in resolve
    raise ResolutionImpossible(e.criterion.information)
pip._vendor.resolvelib.resolvers.ResolutionImpossible: [RequirementInformation(requirement=SpecifierRequirement('Pillow'), parent=None)]

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "c:\python38\lib\site-packages\pip\_internal\cli\base_command.py", line 189, in _main
    status = self.run(options, args)
  File "c:\python38\lib\site-packages\pip\_internal\cli\req_command.py", line 178, in wrapper
    return func(self, options, args)
  File "c:\python38\lib\site-packages\pip\_internal\commands\install.py", line 316, in run
    requirement_set = resolver.resolve(
  File "c:\python38\lib\site-packages\pip\_internal\resolution\resolvelib\resolver.py", line 127, in resolve
    six.raise_from(error, e)
  File "<string>", line 3, in raise_from
pip._internal.exceptions.DistributionNotFound: No matching distribution found for Pillow
1 location(s) to search for versions of pip:
* https://pypi.org/simple/pip/
Fetching project page and analyzing links: https://pypi.org/simple/pip/
Getting page https://pypi.org/simple/pip/
Found index url https://pypi.org/simple
Looking up "https://pypi.org/simple/pip/" in the cache
Request header has "max_age" as 0, cache bypassed
Starting new HTTPS connection (1): pypi.org:443
Could not fetch URL https://pypi.org/simple/pip/: connection error: HTTPSConnectionPool(host='pypi.org', port=443): Max retries exceeded with url: /simple/pip/ (Caused by ProtocolError('Connection aborted.', FileNotFoundError(2, 'No such file or directory'))) - skipping
Given no hashes to check 0 links for project 'pip': discarding no candidates
Removed build tracker: 'C:\Users\username\AppData\Local\Temp\pip-req-tracker-7c3v3app'

上記エラーが出ます。