Long ago.. haven't done it in some time because most manufacturers made it difficult.

I never did it with a new phone because potentially bricking a thousand dollar device didn't seem too enticing.

I also wasn't tech savvy enough to figure out how to unlock the bootloader, so I had to wait for someone else to figure it out and then wait some more to let others test out the procedure.

I use Efoundation E-OS

an android derivative that works and does not need to have a google account

I’ve done it before. Check out XDA developers website and look up your phone model. Depending, the firmware version might be relevant. But as far as I know it’s getting easier and easier. Worst case scenario, you brick the phone and have to buy a new phone or buy a factory cable and flash new firmware. I think even someone of moderate-to-low IQ such as yourself should be able to pull it off.

I have long ago Now I buy rooted phones from a guy who has loads of experience.

Rooting is pretty easy and straight forward now days. Use payload extractor to extract system image, use magisk to patch boot img, then fastboot flash patched boot img, and install magisk app.

Unlocking the boot loader is another issue. Not all phones can be unlocked and without an unlocked boot loader flashing a new rom on the phone can be challenging to say the least. Not always though. I would recommend just using MicroG for Lineage OS. No jewgle and it's compatability list is twice that of any other OS out there. Or you can just install Lineage OS which is compatible with most devices and remove jewgle yourself and add MicroG via magisk.

From there if you wanted to try other OSs without fully installing them you can look into GSI (generic system image) roms. Using a tool called DSU Loader you can boot GSIs without fully installing them and wiping your phone. Whatever you do make sure you do your research first so you don't end up with a brick. Good luck!

XDA forums (xdaforums.com) is a good place to look for info on this subject.