Any usable debugging would tale making an interpreter, which is every bit (excuse the pun) as difficult to do as making the compiler itself. If QB64 were to be used in schools, such a project would be invaluable. A couple of coders, by the way, have tried to produce an interpreter for QB64, made good progress, but ran out of time to complete anything that would work with some tuning. Even if Galleon decided to tackle it, it would slow down advancements in both the IDE and the compiler, and probably take two or more years of development time.
A gimmick trace on program could be built easily enough. you just make a program that reads your existing program from a file, and in between every line adds: DO: xkey$ = LOOP UNTIL xkey$ <> "": IF xkey$ = CHR$(27) THEN END. Of course this could be added as a sub and called in between each line, too.
You could further add PCOPY and switch to a different screen and back, to show the line number being executed. Using LINE INPUT would allow you to step through the original code as the exe file ran it. and waited for each line to be executed with that inkey$ sub or statement.
An alternative is to use the QB64 error line statement, see the wiki, and when you get an error, it will return the line number it occurred at.
Of course, you can always guess, by putting an end somewhere, to see if the buggy code makes it that far. I call that one TRIALON TRIALOFF.
Welcome to the forum,