I just switched to LineageOS 18 w/ MicroG and oh my lord is this stuff still complicated. I'm fairly familiar with this stuff and yet still it took me many hours to set everything up correctly. To be clear, this is not the fault of LineageOS, this is simply the state of the FOSS Android environment and the fact that Google has no interest in supporting this setup whatsoever, to put it mildly. Not only is it complicated, it also seems to change pretty much every year.
First the question is how to transfer all your application data, for which there still seems to be no surefire way. I settled on "Neo Backup", which mostly worked fine, except for Signal (of course...), and the darned Microsoft Authenticator.
So first unlock the bootloader (good luck), then you need to find the correct TWRP for your phone (and careful with 32/64 bit) and flash it via fastboot.
Then I flashed LineageOS, which worked fine. Luckily I found an image which already had the signature spoofing patch included, so I didn't have to worry about that. How do you get root? SuperSU? XPosed? Magisk? OK it seems everybody's using Magisk nowadays. OK, flashing worked fine, but now, how do you get MicroG on it? If you look at the MicroG homepage, you might think you can just install it with F-Droid, and you actually can, but many things won't work (like FCM notifications). It needs to be a system app. I tried using the F-Droid Priviliged Extension, flashed it via TWRP, which seemed to work fine but actually wasn't installed and not working at all. Now what? There's a multitude of information in forums what to do. Some say to flash NanoDroid, but the last release was in January 2021, it seems it's not updated anymore? I settled on the "MicroG installer revived" Magisk module, which worked fine (btw, there's no curated Magisk module repo anymore, you have to search the web and hope you find something that's not malicious).
Of course my banking apps refuse to run because "U ROOTED UR PHONE", I search for Magisk Hide, it doesn't exist anymore, now you need to configure a "Zygisk deny list", whatever that is. Then I also need to hide the Magisk app, my banking works now thank you very much. FCM notifications also work after I uninstall and reinstall my apps which need it...
To be clear: I'm eternally grateful to all the developers who make this possible in their spare time. This is not their fault.