Yes, just build your own on Linux or choose a Linux distribution that keeps current. Either solution works. There are step by step instructions for building your own from Source on Linux in our Repo.
You did not say which Linux distribution and version you are using. Looking back I think you said OpenSuse. If so you can just grab their Sigil-1.9.2 version or file a bug report with them and ask their Sigil maintainer to cherry pick the same patches that Arch has for working around gcc -flto issues.
But that said, based on this link, a fixed version of Sigil 1.9.10 for OpenSuse is already available. See the last post here:
https://forums.opensuse.org/archive/.../t-570506.html
So updating to that version using your package manager should make things work.
As for the flatpack package, it sounds like issues with the pcre2 version not being available or not working. I have not run into that. You might want to alert the flatpak builder and file a bug report with them in case it can be fixed.
Alternatively, Calibre has its own ebook editor as part of its ebook library management series, and Calibre maintains its own builds for Linux. You could give it a try.