It seems reasonable to me to backport the fixes to 43 as they are bugs. (note: I’m not a GNOME dev)
I think the easiest way is to use nightly for now. For PDF files, you can preview them using the spacebar if it is ok for you.
I tried to build 42 as a flatpak, but I have errors (also, even if it was a success, I will not have the PDF thumbnails). I didn’t try installing the non-flatpak version (I didn’t do that). But if you really want to do that, better to wait for a dev comment to guide you.