I have the same problem. Extremely annoying. Only in 2021, It did not happen in previous versions. Now I have the habit of saving the file after every few segments. (Auto save only worsened the situation as if you have a segment change concurrently with saving, that is a crash for sure - this was a hint in one of my previous posts about this issue here).
I thought it was related to spell checking but even disabling it will not prevent crashing.
It seems to be related to large TM only though.

I am often upset by this. If is surely a bug for long time but there has been no fix, no update. I am absolutely sure I will not pay for a new version just to avoid this! 

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The large TM may be a factor here. Where is it stored? If you have it on a drive linked to OneDrive or in some other cloud solution and have not made sure that what you see isn’t just a footprint because it will need to be downloaded every time you use it then the problem could be due to this.

a bit more information would be helpful because these days it’s increasingly more complicated to work on a PC efficiently and many users just want a plug and play and are not aware of the implications of other features they use on their computer.

 Tamás Donát 

The large TM may be a factor here. Where is it stored? If you have it on a drive linked to OneDrive or in some other cloud solution and have not made sure that what you see isn’t just a footprint because it will need to be downloaded every time you use it then the problem could be due to this.

a bit more information would be helpful because these days it’s increasingly more complicated to work on a PC efficiently and many users just want a plug and play and are not aware of the implications of other features they use on their computer.