UPDATE - PROBLEM SOLVED: I do not know what was wrong, but I solved the problem. I am going to post anyway, in case someone else has this problem, too. Solution: I copied the data and pasted it into a new spreadsheet, using Paste Special - Unformatted Text. The problem is gone.
I did some experimenting after finding the solution. Cutting and pasting my column as unformatted text within the same file also worked. Cutting and pasting without Paste Special did not work.
PROBLEM: This Calc file has exactly one column, with about 600 fields full. The column is formatted to text only. The column is just email addresses. To the best of my knowledge, I have removed all hyperlinks in the email addresses. (I’m going to post a separate question asking if there is a way to do this globally.) There are no graphics, no calculations, no macros. When I am typing in a new field, the characters do not appear immediately after I type them. Scrolling is delayed by seconds. It is challenging to add new fields.
I also use Impress and have some big slide shows with 100 slides with pictures and words. I have no problems with that running slow.
Equipment: new Windows 11 Lenovo laptop.