I've recently started doing crude drawings on my reMarkable when needing something like explainer diagrams. It looks like a toddler did it, but, you know what? It works. I just stopped feeling weird about it.
Pen-type input systems are pretty cheap these days (no need to go reMarkable, I just use it because I have one.) It's not a super frequent need but having something of that type in general I'd consider valuable enough to spend the money.