Links and ipad

Greetings all!
My issue is perhaps addressed elsewhere; but I couldn’t find any relevant posts. I am having difficulty understanding how to use links in Excel on iPad. Sometimes the Insert Link button is greyed out while other times it is available even though there are no links already in my selected cell either time. I would appreciate:
1. Some help in understanding what I am doing incorrectly; and
2. Suggestions for good tutorials for using Excel on both iPad and Windows 11.
Thanks much!
Dave