I have been using Hail with Shizuku for removing most of the Samsung and Google apps, replacing them with Foss alternatives but I would love to know that when it's time to retire this phone or I stop using Google services, is there an easy way to install custom ROM on this phone?
There is not official rom support for this device and only can find an unofficial rom build for the 5G version of this device.
Once you retire the phone, I would get a Google Pixel phone and flash GrapheneOS on it personally, even though your buying a phone made by Google themselves.
If you are unable to install a custom ROM on your Samsung smartphone, the next best alternative is probably to use https://github.com/0x192/universal-android-debloater to deactivate as much Google and Samsung spyware as possible.