u/Card-Crazy-77

I have a toilet that is not clogged but is not flushing properly. It generally disposes of the waste (or the vast majority of it) but doesn’t make that “flushing sound.” It confuses me because every so often it *will* make the sound. The frequency of the normal operation has decreased over time.

Is it a flush valve problem? If not, what are some amateur DIY fixes I can try before calling someone more experienced?