What could cause frequent toilet clogs? It is not the usual suspects
Since you have already replaced the toilet, we know its not that. Just because the sinks and tub don't have a visible problem, doesn't mean it's not a vent issue. The water flow rate is significantly lower on those, so the potential to pull a vacuum because of POOR air flow through the vent is not there. But the big rush of water from a toilet flush needs a big slug of replacement air from the vent to avoid pulling a vacuum and if there is a bird or rat nest in the vent pipe that restricts that flow, but doesn't totally block it, that will only show up after the toilet flushes.