Well, this is what appears to be the case in my Studio 2019. Despite changing it to Default every time I use it, next time I launch the program I get Flags and I have to change it again!

I don't think the Flags Layout is the default. (As the name suggests, it's the Default Layout that is the default). Studio/MultiTerm remember the last layout being used and I assume you used the Flags Layout at some stage and now it is remembered. Anyway, we'll leave this one in Under Community Review for now.

No professional/productivity-oriented software should prioritize mouse actions over keyboard actions in its design. The mouse is for the people who use the computer for... leisure.

I totally agree with you. In general the editor of SDL is an "old hat" and contains many grave errors.

But back to the problem with the computer mouse. My suggestion to SDL is, take away the mice from the testers!!! Then you will see how well the editor of SDL really works!