You said it like banking apps will be happy to work with a Linux phone lol, and rooting and getting a custom ROM (one which exists or otherwise) are two completely different things that have nothing to do with each other, and you shouldn’t support manufecturers who choose to make it difficult to unlock bootloader anyway.

By 2025, rooting still empowers you to make your own Android device however you like it to be.

Also not many people care about custom ROM these days because Android stock ROM got much better in average, so there’s much less a need for creating a brand new ROM just to get basic features. Why making a brand new ROM instead of modding the pretty good one you already have now. And root empowered ROM modding tools that are developed as Magisk module or Xposed modules still have a pretty big community, there’s a long list of pretty big repos with hundreds of modules each, and with how sophisticated Magisk and Lsposed have evolved it’s easier than ever to write your own mods