For me as a desktop linux poweruser, I find this potential transition pretty intimidating, I've never flashed a phone with a custom rom let alone switch to a completely different OS, and I am not sure if the phone can even be reset to its original OS, if things go south.
It's relatively easy. It's basically a command for each step you want to do and it tends to fail gracefully nowadays.
If you can install a linux distro you can flash a custom rom on a well-supported phone.
If it were more mainstream I could see GUI apps to manage all this for people, if they don't already exist. Idk I just use adb.
Don't worry if you're not ready, just as on the desktop, there are pioneers ahead of you that will clear the way <3
/e/OS at least has a browser based installer[0] for quite some supported phones. I definitely recommend trying it out, installing a custom os on my phone gave me the same feeling when I first ran debian on a laptop struggling under windows (even though the performance gains aren't that apparent in my opinion).
[0]https://e.foundation/installer/