Your profile shows you already have Office 2019 so try to get a course with that uses the nearest to that so that there will be as little difference as possible when you practice at home.

Also remember that Excel is for those who have mathematical knowledge and are computer savvy to translate formulae into Excel input. I assume you have both these traits? If not you will struggle. If you have then, as Pecoflyer says, it's practice, practice and more practice for however long that takes.

I have been dabbling in Excel for 20 years but because one only learns what one needs to learn to achieve the job at hand it is easy to see that one cannot know how to do everything that Excel is capable of.

Good luck.