As far as I know, the layout has only significantly changed in version 115, which would be once in the last three years. Can we examine please, which part of the UI has most impacted your use of Thunderbird?

First of all, Thunderbird, with out even asking, put all of my replies in subfolders. It took a while to find out how to disable this. In the mean time I went through hell looking for replies. Now I am continually badgered with updates. Also, apparently, this next update is even worse. I do not need it, do not want it, and will never upgrade to it. I am now in the process of installing an earlier version that I will never upgrade. If Thunderbird really wants to do it right with upgrades then give us a choice to ignore layout changes and never change layout options without asking. That is arrogant and rude! I am insulted by Mozilla's attitude. I do not need calendars, schedules or anything else messing up my menus and layout. The earlier version has all I need. I hate to say it, but I have not been able to find a suitable replacement for Thunderbird. If I could, believe me, after what they did, I would not even use an earlier version. I'd drop them like a rock. I do not need to be pissed off every time I open my email.