Given the general nature of the question, my general advice:
- Back up
/home to an external drive, unmount that external drive, and unplug it from your computer;
- Download the ISO of whichever version of Ubuntu you'd like to install, verify its checksum, and burn it to a flash drive;
- Follow these instructions to create a new
/home partition and copy your data to it. This page is also useful;
- Reboot to assure yourself that step #3 worked;
- Assuming all is well at that point, plug in your flash drive and boot your computer from it;
- When it's time to tell the installer to partition your drive, choose "something else". You'll have to tell the installer to mount your old partition as
/ and format it and to mount your new partition as
/home and do not format it; and
- Finish your new installation as usual.
If you use
/var for any sort of data, such as running a Web or mail server, consider doing the same thing with
/var as with
/home. I don't, but if I ran a server, I would.
I made a separate
/opt partition because I install several programs from source and run a few programs from appimages and java archives. It's nice to be able to have them up and running immediately on a new install. I'm the only user on my computers, so if I had it to do over, I'd probably just put it all in
Ordinarily I'd advise backing up
/etc and restoring it too, but your objection to your current install makes me think you'd be better off starting over. I'm considering making a separate
/etc some time before the next LTS comes out. It never bothered me before, but this last install (22.04.01) did. The more I tinker with Linux and learn about it, the more I lose by not planning ahead.
Following the belt-and-suspenders rule, you might also consider backing up your configuration files to a (for example) GitLab or privately-hosted remote git repo. Here's the instructions I followed. Another advantage of this is that you can set up an account on another computer and rather quickly make that new account comfortable.
This might seem a bit complicated, and it is. But it's one of those things that you do once and it's done and, from now on, every time you reinstall you'll be glad you took the time.