You may want to skim this thread in the forum. Some recommendations are also made there, though it is a bit dated now. I recommended an Introduction to Linux course, though I never took it myself.
I concur with the suggestions above to create a ‘cheat sheet.’ I have a file where I keep the Linux commands that I do not use often enough to remember but are useful sometimes.
One thing to be careful of: Linux distributions want to change little things here and there. When you do a search on how to do or fix something, always include ‘debian’ or the graphical interface in the search. Otherwise, you’ll get suggestions on other distros or GUIs that implement things differently. Those files or settings may not exist on your system, etc.