RVM, where is Ruby 3.0.0?

In many parts of the world, the current time is holiday time. RVM is maintained by unpaid volunteers in their spare time, who might choose to spend time with their families.

Therefore, it might take a while for a new release of RVM to come out.

Also, there are a couple of bugs related to YARV 3.0.0 not working on the RVM bug tracker, obviously those will need to be fixed before a new release of RVM that supports YARV 3.0.0 can be released.

If you have not updated rvm do that first RVM Upgrading

rvm get stable 
# or 
rvm get master # for even newer versions not in stable 3.0.0 in this case

To see all available rubies run

rvm list remote all 
# or
rvm list known # as pointed out in the comments

you should see ruby-3.0.0 in the list of available rubies

Then run

rvm install ruby-3.0.0