Install ruby 3.1.0 with rbenv on OSX Monterey 12.5 Based on hours of fiddling and trying everything I could find and can think of. This is the config which worked for me.

Install-ruby-3.1.0-with-rbenv-on-OSX-Monterey-12.5.md

Install ruby 3.1.0 with rbenv on OSX Monterey 12.5

Based on hours of fiddling and trying everything I could find and can think of. This is the config which worked for me.

1) You need to set these exports

# ruby
export PATH=/Users/jan/.rbenv/shims:$PATH
export optflags="-Wno-error=implicit-function-declaration"
export CFLAGS="-Wno-error=implicit-function-declaration"
export LDFLAGS="-L/usr/local/opt/libffi/lib $LDFLAGS"
export CPPFLAGS="-I/usr/local/opt/libffi/include $CPPFLAGS"
export PKG_CONFIG_PATH="/usr/local/opt/libffi/lib/pkgconfig:$PKG_CONFIG_PATH"
export CONFIGURE_OPTS="--with-openssl-dir=$(brew --prefix openssl@1.1)"

# ruby-build
export RUBY_CONFIGURE_OPTS="--with-openssl-dir=$(brew --prefix openssl@1.1) --with-readline-dir=$(brew --prefix readline) --with-libyaml-dir=$(brew --prefix libyaml) --with-zlib-dir=$(brew --prefix zlib)"

# ruby - readline needs this
export LDFLAGS="-L/usr/local/opt/readline/lib $LDFLAGS"
export CPPFLAGS="-I/usr/local/opt/readline/include $CPPFLAGS"
export PKG_CONFIG_PATH="/usr/local/opt/readline/lib/pkgconfig:$PKG_CONFIG_PATH"

# ruby  - openssl needs this
export LDFLAGS="-L/usr/local/opt/openssl@1.1/lib $LDFLAGS"
export CPPFLAGS="-I/usr/local/opt/openssl@1.1/include $CPPFLAGS"
export PKG_CONFIG_PATH="/usr/local/opt/openssl@1.1/lib/pkgconfig:$PKG_CONFIG_PATH"
export PATH="/usr/local/opt/openssl@1.1/bin:$PATH"

There is discussion onlie if you can concatenate LDFLAGS with a :or an .

2) You need to make sure your openssl path is correct

Check which opensl. The rbenv install only worked when it was set to /usr/local/opt/openssl@1.1/bin/openssl.

This is why you need to set export PATH="/usr/local/opt/openssl@1.1/bin:$PATH"

Having these things taken care of rbenv install 3.1.0 succeeded without a problem.