@georgia the truth is, TWRP is kind of janky. I've had several installs of it that gave me corrupted backups.

You should be using a MicroG supporting unofficial build of Lineage instead of trying to make it work with xposed. Xposed is janky as fuck, I don't use it anymore, haven't in many years.

If that isn't an option, follow some instructions to the letter and patch it yourself for sig spoofing. It isn't that hard, it is confusing though.