Thu Aug 26, 2021 8:53 pm
As long as you don't have any checked luggage and the first flight is on time, it should just barely be doable. Keep in mind that gate-checked luggage counts as checked luggage too and just like ordinary checked luggage you have to retrieve it at the belt. However there's no time for that, so make sure to keep your luggage with you at all times. Maybe it's worth buying priority boarding for your first flight so your large hand luggage is allowed in the cabin.
Vienna is a pretty straight-forward airport with mixed arrivals and departures. Unfortunately Ryanair sometimes uses remote stands with a bus to the terminal, in which case you're dropped off straight at the arrivals. In that case you have to run to make it to departures and clear security again, back to the departure gates. And that is if the flight is on time, if it's late this might cause you to miss your connecting flight. If your first flight arrives at a gate you got more time, you can just go straight to your departure gate which should be in the same part of the airport. No need to walk far.
Nonetheless it's a connection I would be weary about, there's a good chance of missing it. I've self-connected quite a bit but always with a few hours in between. So far it always went fine but such short connecting times could be just asking for trouble.
Have you considered other possibilities? By the flight times you're stating I was able to figure out you're planning to fly on Friday. I found a rather cheap opportunity on Wizzair and Norwegian on Friday from Athens to Copenhagen self-connecting in Budapest on Friday with 4 hours in between the flights. That's a connection you should certainly be able to make.