Thunderbird not responding, reinstall/safe mode not helping

After a reboot and Windows 11 update today, Thunderbird (I believe it was v155) will not open. It asks for the password, then sits at [Not Responding]. I have copied my profiles (there are two, one dated 2023 with only a 1K .json file in it, and one created tonight while I was troubleshooting that's several GB and when copying, appears to contain all my mail folders although I can't access them directly from within the profile) to a separate location (my desktop). I've tried the following (after checking previous questions here in Mozilla support): (1) booting Windows into safe mode (2) opening Thunderbird in Troubleshooting mode (Shift while opening), both in Windows safe mode and normal boot (3) uninstalled Thunderbird from Control Panel, downloaded and installed a new copy of Thunderbird All give the same result: "not responding", can't click anything. Can only wait or close. I was able to disable an extension that I installed yesterday that had been working fine. I'm also wondering if the problem is mail folders that are too large. I have some candidates for deletion but since I can't see any .msf files for them, I can't delete (because I can't open Thunderbird. I'm leery of instructions to outright delete any Thunderbird folders/files because (1) I can't see my mail folders directly and (2) I'm self-employed and all my client and business emails are in there. Losing them woud be a disaster. I'm tempted to try the Windows option of restoring my entire computer to an earlier point, say, this morning. But that seems like possible overkill if it's an issue with just Thunderbird. I'm freaking out, please help!