Toilet does not flush, pressure is non-existant, it worked when first installed, what's up?
Given all of the steps you have already done I would go the cheapest and most effective route.   Get a couple gallons of muriatic acid (big box).
Pour about a 1/5th of the container down the tank drain - directly.   Let it sit 3-4 hours.   Flush and repeat as many times as you can.  You need ventilation in the room, you will not be able to use the room at ALL during this process, and this will effectively destroy anything blocking any &quot;holes/drains&quot; in your toilet.    I have effectively spent $5-10 and restored 50+ toilets to like new condition using this method, some not draining at all.
Wear gloves and goggles and wash off anything that gets on your right away.   Do not leave these containers around small children.