Gem::Ext::BuildError: ERROR: Failed to build gem native extension on macOS Monterey

When I run bundle install on my rails 5 project, I am getting a number of errors on gems that appear to have native extensions. Here is the top of the output for one of those gems:

Installing nio4r 1.2.1 with native extensions

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

checking for unistd.h... yes
checking for rb_thread_blocking_region()... no
checking for rb_thread_call_without_gvl()... yes
checking for sys/select.h... yes
checking for poll.h... yes
checking for sys/epoll.h... no
checking for sys/event.h... yes
checking for sys/queue.h... yes
checking for port.h... no
checking for sys/resource.h... yes
creating Makefile

current directory: /Users/<my-username>/.rvm/gems/ruby-2.7.4/gems/nio4r-1.2.1/ext/nio4r
make "DESTDIR=" clean

current directory: /Users/<my-username>/.rvm/gems/ruby-2.7.4/gems/nio4r-1.2.1/ext/nio4r
make "DESTDIR="
compiling monitor.c
monitor.c:91:24: warning: '(' and '{' tokens introducing statement expression appear in different macro expansion contexts [-Wcompound-token-split-by-macro]
if(interests_id == rb_intern("r")) {
                   ^~~~~~~~~~~~~~
/Users/<my-username>/.rvm/rubies/ruby-2.7.4/include/ruby-2.7.0/ruby/ruby.h:1847:23: note: expanded from macro 'rb_intern'
    __extension__ (RUBY_CONST_ID_CACHE((ID), (str))) : \
                  ^
monitor.c:91:24: note: '{' token is here
    if(interests_id == rb_intern("r")) {
                       ^~~~~~~~~~~~~~

I have tried a number of things.

Per this post I tried the following suggestions:

# didn't fix it
bundle config build.nio4r --with-cflags="-std=c99"
bundle

# didn't fix it
xcode-select --install
sudo xcodebuild -license accept
bundle

I also referenced this Go Rails guide, specifically the "Final Steps" section that deals with gems that require C extensions, but that command seems to not apply because I didn't migrate my macOS from Mojave.

At this point I'm not sure what to try next. Ultimately: it appears the issue revolves around being unable to install gems that require C extensions.

Environment:

macOS Monterey version 12.2
Using rvm with ruby version 2.7.4
Project is using rails version 5.0.1

Solution

It turns out the problem was that in the Gemfile.lock file, it was locked to using an older version of bundler. We simply deleted the Gemfile.lock, and re-ran bundle to regenerate Gemfile.lock. That solved it. It now says this at the bottom of the Gemfile.lock file, so it liked this version of bundler:

BUNDLED WITH
   2.3.9