Asterisk 11 is almost 10 years old and hasn’t received any bug fixes in almost a year. It will be completely EOL with no security fixes in October 1.
With that said it should be a valid expectation that 11 support will be dropped in upcoming releases. That doesn’t mean 11 won’t work it just won’t be supported. The time is now to move up. 13 is the current LTS version of Asterisk.
From what I have seen the only reason to not move to 13 is an edge case on queues which is about to be resolved.
FreePBX 14 is in the final stage of testing and will still support 11. Some modules and features do require Asterisk 13+. If you have a test environment where you are testing FreePBX 14 for production use or test in general I recommend updating that environment to Asterisk 13 to ensure it meets your needs for the future. Distro users may run asterisk-version-switch and update to 13 without any effort.