I've been working with Excel since 1995. I haven't taken any courses in Excel, but when I changed jobs several years ago, I had to work with long documents in MS Word for the first time. I knew Word basics, at least an old-school version of things, but had lot to learn and refresh myself on. I found that the courses offered by LinkedIn Learning, which has a free trial month, were pretty good. I can't speak for the Excel ones very much, but if they're of the quality that the Word ones are, they're a good start. I paid for a subsequent month (it was a lump fee, like $25) and took some additional courses for a while. I think that might be a nice start.

Additionally, I'm finding some YouTubers are an excellent reference, and a place to pick up ideas on how to better do a task. I follow Leila Gharani, Mynda at MyOnlineTrainingHub, ExcelIsFun, and sometimes I just search YT on various subjects related to Excel. Leila had my intro to some of the new Excel 365 functions.

Ann