System integration not responding, preventing access to Thunderbird

My problem is that I can’t get into Thunderbird because each time I start it up I’m presented with a window that says "System Integration" (Not Responding)" and I have no way of making progress – all I can do is use Task Manager to exit TB. The “system integration” window first appeared a few days ago and initially I was able to dismiss it by choosing the “Skip integration” option. Today was the first time it became unresponsive. No changes have been made to the system and TB should be up to date – though, not being able to open TB, I can’t check the version number (probably esr). I have used TB for many years and have it installed on two PCs, both running on Windows 11. It’s working as normal on the other computer. I’ve tried rebooting the computer, to no effect. I’ve also tried to open TB in troubleshooting mode but can’t get past the "System Integration" (Not Responding)" window. It’s been a couple of months since I backed up so I’m really hoping there will be a solution that preserves all my emails, address book and calendar. I’d be very grateful for any suggestions.