I know what you mean; I'm finding the same. A friend who writes this short Googles 'free to submit anthologies 2021' (or something like that). She aims for those publishing in paperback carrying an ISBN, and then registers the title & ISBN with the Authors Licensing & Collecting Society. Payment is very much better and acrues. Not sure if you need to be in the UK, or a UK citizen, for this. But you can look it up.