First of all, the clutch is NOT part of the transmission.
There is no simple answer to your question. Some automatics last “forever” and others fail before 100K miles. It depends on the make, and how the transmission was maintained.
In my opinion a manual transmission has the potential to last much longer than an automatic. I still prefer manual-transmission cars, and, like you, have never had to replace a clutch, even at nearly 200K miles. But, again, the clutch is NOT part of the transmission. It’s a wear item, and sooner or later you will have to replace a clutch.