I've used Replicant, CyanogenMod, LineageOS and GrapheneOS.
I think it hasn't actually gotten easier IMHO - but some manufacturers are decently chill about letting customers own the hardware they paid for (Google!), others are nightmare-mode dystopian parodies (Xiaomi, but also late-model Samsungs).
The Pixel is really the only option for custom ROMs here in the US, as far as my experience goes. I stood in a local electronics store and went down the list of Lineage supported devices and couldn't find a single one with the EXACT model number, which is required, for a given brand. I checked over 20 devices. I did find some devices online but the vendors make it nearly impossible to obtain their driver packages. Motorola requires a horribly massive package, drivers, admin privileges, an online account, and you can ONLY flash from the tool. You can't select or save a ROM file. It's aweful and full of flash ads like late 2000s websites.
