You can follow the 3.5.3 to 4.0.0 instructions which are here. Just remember to do git checkout v4.0.2 instead of git checkout v4.0.0.

It says in the instructions that:

The recommended Ruby version has been bumped to 3.0.4. You can upgrade, or you can continue using the old version by overwriting the .ruby-version file with e.g. 3.0.3 which was recommended previously

To upgrade the version of ruby to 3.0.4, I followed these instructions:

cd ~/.rbenv/plugins/ruby-build
git pull
cd ~/.rbenv
rbenv install 3.0.4

This took maybe 5-10 minutes to run, so be patient!

I then went back to the official instructions starting with

bundle install
yarn install

Overall it was a nice and painless upgrade!