I have a very vague familiarity with how it works, but I don't think there are alternatives. If you're using Wayland, you either have to rely on a distro or DE to configure it for you, or do it yourself.
To be fair: I don't think the idea behind portals is necessarily bad. But the half-baked implementations that all do things slightly differently is a pretty bad UX overall.
Is there some way to avoid such a mess (and other problems with XDG portals and other XDG stuff) by substituting a .so file, somehow? I don't really know enough about how it works to know whether or not such a thing would work. (Maybe it might work for some programs, depending on which libraries they use for this purpose.)