My Pixel 4a is getting its software support dropped, meaning no more security patches and increasing vulnerabilities. So I installed LineageOS for microG, a fork of LineageOS that has microG. I chose this one because LineageOS has good support for "older" devices like mine unlike GrapheneOS, and getting microG bundled in the fork is a turnkey solution for getting me access to Google services when I need them.
The installation process itself was very simple, I just followed the guide on the LineageOS site and ignored the optional stage for installing a GApps package since I already had microG. The pre-install work was more complicated, and required downloading a few tools and drivers for the Android Debug Bridge (adb) to work. I think this is the biggest barrier to entry - if you can get everything set up for the install, you shouldn't have any trouble with it.
After loading in and getting basics like Wifi and fingerprint lock set up, I was off to the races. The install comes with a very lean set of FOSS apps, as well as F-Droid to grab more. I immediately went and got Aurora Store off there so I could access the Play store and all its apps, which worked without a hitch. In fact, everything I've installed has worked as well as I would expect with the stock ROM with the exception of Google Contacts, which would not sync from my google account (and I can't even definitively say this was a ROM-related issue). Even my banking apps work despite my device not passing the SafetyNet check. Your mileage may vary depending on your apps and their requirements, but I myself was pleasantly surprised. The only thing I think I'm losing out on is NFC payments using Google Pay, but that's not a big deal for me.
Barring that one exception, everything just works and I'm glad I went this route. I was already happy with my Pixel 4a, and buying a whole new phone just because Google decided it couldn't be bothered to update it anymore would've left a bad taste in my mouth, especially as I'd be giving up features (headphone jack and fingerprint sensor on the back) I value. Now it's time to ride this baby out for as many more years as I can.