I did not upgrade our mastodon server to 4.2.0 from 4.1.9 for a long time. Finally while doing so in the morning, I got the following error with the bundle install command.

Your bundle is locked to json-canonicalization (0.3.2) from rubygems repository
https://rubygems.org/ or installed locally, but that version can no longer be
found in that source. That means the author of json-canonicalization (0.3.2) has
removed it. You'll need to update your bundle to a version other than
json-canonicalization (0.3.2) that hasn't been removed in order to install.

I have no clue about how Ruby works, but somehow only updating the lockfile via bundle lock --update json-canonicalization did not help. Finally updated the Gemfile.lock file to have json-canonicalization (0.3.3) manually. That solved the issue and I could continue with the update steps.