"with fixed split doors with side hinges."

"Fixed" as in they do not open?

They sag and don’t open at all in a very short time.

As said above they sag and are hard to open. Your probable response will be they are rarely open. In my experience that as they age, it is nearly impossible to keep them sealed. This will allow gaps around the doors and all kinds of wild life into the garage. Also It will be difficult to have window in the doors, limiting the natural light in the garage.

You could get a stable door in steel or aluminum with a steel frame. Custom unless you weld.

I suspect you'd have some challenges with hardware with enough security and beefiness. (and sealing issues too.)

In general, if it's not being done en masse - it's for a reason.

And what about an opener? even in occasional use.

My inlaws had a huge fixed panel door that used a standard opener and some huge springs - but it allowed a very custom soution for a stone barn from the 1700's converted into a garage - where a traditional roll up door would have looked terrible.