I guess I have to give up and just use my working backup. My phone can afford the storage space. I looked into the flatpak install, but I don’t think it would work because ARM isn’t listed under supported architectures, though I haven’t tried it.
To summarize the problem and what I’ve tried: The segmentation fault happens when trying open my large collection, but does not occur on a small test collection. It occurs in fresh installs of Debian 11, Debian 12, Ubuntu, and Arch, all installed in a PRoot environment in Termux. It does not occur in my Debian 11 backup, but apt/dpkg is broken in this backup due to a botched upgrade.
I don’t think there’s many users out there using Anki in a PRoot on their phone. If there’s someone out there wanting to do it, I can provide my backup file. It’s 3.5GB compressed though