They eventually stop, Excel has a max column size of 16,384. Not sure what letter combo that would be (ZZZZZZZZZZ or something?), but it does eventually halt.

https://support.microsoft.com/en-us/office/excel-specificati...

Not even close, column 16,384 ends at XFD. [0].

[0] - https://learn.microsoft.com/en-us/answers/questions/4888467/...