The most likely cause and also the easiest solution to the problem is
to replace the wax seal. I have to do this for my toilet every two
years or so. My toilet is over the washer dryer and I suspect the
warm air from the dryer softens the wax seal causing it to lose its
seal integrity. The little air it lets in during the flush cycle
weakens the siphon action. The crap and the toilet paper barely gets
sucked out, and if there is a slightly larger load, they form a dam
and result in a messy overflow. Put in a new wax seal. If that fixes
the problem you know what to do in future. If it doesn't you are not
out by much in cost or effort.

Reply

true that might fix it but also the bolts may break, flange may have a
problem etc.

ONLY pull toilet after less invasive means have been attempted and
failed...

TRY using only a full bucket of water to flush, if it works ok every
time then its the toilet