It would seem so. I made the mistake of purchasing it for $25 a little over a month ago, but only just recently started using it, only to find the app doesn't work properly under Big Sur. I've tried to get in touch with these people to see if there is a fix or known bug, but no answer.
I've asked for a refund. No answer.
I've managed to solve one of the problems by editing the .nib file itself, but the stupid program still doesn't remember what documents were open, where I was in the document or the document layout (drawers, tabs etc).
These are not even *features*, just basic requirements for all apps.
I guess I will try to get a refund through my credit card, but I'd much rather have a working app.