This page lists the main places where you can submit bug reports, ideas and other comments. If you want to suggest an idea or report a bug, it might already have been discussed somewhere, but duplicate suggestions or reports are okay.
The VVVVVV Discord has a #ved channel! You will probably get the quickest response here.
You can report bugs and suggest ideas, and vote for others' reports or ideas here. Does not require account registration.
There is a board dedicated to discussion about Ved on the tOLP forum. Suited for discussion and questions, but also for suggesting ideas and reporting bugs, since topics can be marked as solved.
The repository has a section where you can create Issues, if you have a Sapphire/ account.