If you want to keep on FR 11.20, you then would just have to install the maintenance release 85 which is the latest one for 11.20 btw. 

Refer to: 

Hi, 

For log4j we need to patch anything or our preset version is enough for log4j Vulnerability.

Thanks 

You are running a long term support feature release 11.20 and you do not have to upgrade right now. Normally what I do is to take a look if there is anything that fix an issue on a particular agent/feature within a maintenance release or feature release, then decide whether I want to upgrade it or not.

Also, personally I prefer to jump to from LTS to LTS and avoid in between versions such as 11.21/21 or 23, but this is just me. Anyways.

Since you are running 11:20 which isa Long Term Support version, you could either jump to the next LTS available version which is 11.24

Here is all the details on whats new in that version: Newsletter for New Features in Feature Release 11.24

And here is a great post from @Mike Struening on the Best Practices while upgrading your environment

Enjoy