Ultimately the custom ROM support for Sony phones is pretty lacking due to their tiny marketshare. For instance there are no official LineageOS builds for any of their recent releases.
I'm using LineageOS 19 (with microG) on my Sony XA2 :) Well supported.
Or do you mean Sony's latest device releases? The open firmware program is only for the midrange devices like the Xperia 10 and XA series before that, and of course it depends on having a maintainer. And new devices take time.
