Pythonの環境構築

前提・実現したいこと

初心者です．pythonの環境構築をしようとhomebrew→pyenvとダウンロードしたのですが，その後python 3.6.5をダウンロードしようとすると以下のようなエラーが出てうまくダウンロードできません．どうすべきか教えていただけないでしょうか．mac osはBig sur ver.11.1です．

pyenv install 3.6.5
python-build: use openssl from homebrew
python-build: use readline from homebrew
Downloading Python-3.6.5.tar.xz...
-> https://www.python.org/ftp/python/3.6.5/Python-3.6.5.tar.xz
Installing Python-3.6.5...
python-build: use readline from homebrew
python-build: use zlib from xcode sdk

BUILD FAILED (OS X 11.1 using python-build 20180424)

Inspect or clean up the working tree at /var/folders/n9/7n9khcyj31g91y458qtlvdmw0000gn/T/python-build.20201225100604.39322
Results logged to /var/folders/n9/7n9khcyj31g91y458qtlvdmw0000gn/T/python-build.20201225100604.39322.log

Last 10 log lines:
./Modules/posixmodule.c:8210:15: error: implicit declaration of function 'sendfile' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
ret = sendfile(in, out, offset, &sbytes, &sf, flags);
^
clang -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include -I/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include -std=c99 -Wextra -Wno-unused-result -Wno-unused-parameter -Wno-missing-field-initializers -I. -I./Include -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/usr/local/opt/openssl@1.1/include -I/Users/Raymond/.pyenv/versions/3.6.5/include -I/usr/local/opt/readline/include -I/usr/local/opt/readline/include -I/usr/local/opt/openssl@1.1/include -I/Users/Raymond/.pyenv/versions/3.6.5/include -DPy_BUILD_CORE -c ./Modules/pwdmodule.c -o Modules/pwdmodule.o
./Modules/posixmodule.c:10432:5: warning: code will never be executed [-Wunreachable-code]
Py_FatalError("abort() called from Python code didn't abort!");
^~~~~~~~~~~~~
1 warning and 1 error generated.
make: *** [Modules/posixmodule.o] Error 1
make: *** Waiting for unfinished jobs....