When I flush, the water swirls & goes down but up comes some material of the flush.

I've tried:

Making sure all holes under the rim and on the bottom of the bowl is clear.

Tank fills 1/2 below the top of the over flow tube

Dis you check the jet to be sure it wasn't blocked with minerals?

You may also have some blockage or even a wax seal that is bulging over. Try using a towel bowel rodder or plunger, If that still doesn't help then pull the toilet and inspect. You can also do more rodding at this point with the bowl removed.