Thunderbird on Ubuntu 22.04 keeps "not responding" sometimes locks up pc

Running Thunderbird 140.2.0esr (64-bit) on Ubuntu 22.04. Both Tbird and Firefox are frequently hanging with "not responding" message. Sometimes if I "wait" it responds again. But I often have to Force Quit. Sometimes all apps, the cursor, everything hangs completely. A couple of times, I've had to reboot to continue. This has happened far more often in the last few months than it did previously. It can happen after opening new mail or after opening mail saved in Local Folders. I run updates as often as I am notified that they are available. The only extension listed is Import Export Tools. I just disabled that, since I wasn't aware that it was running.