The bananaphone has the developer menu disabled by default, though you can do a magic key combo or a filesystem fiddle to bring it back, although I think Nokia didn't actually want this, so they may lock it down if they're releasing new devices. With the dev menu unlocked you get the ability to sideload PWA apps onto the device, and also get usb debug to the underlying Android bits. But I don't believe the bootloader is (or can be) unlocked, so I guess you're stuck with KaiOS.