The fact you want to drive fighter jets basically rules out all sensible electrical power options. Without a ready source of atmospheric oxidiser, fuel cells have no particular benefit over batteries and batteries just don't have a high enough energy density to let you do any fancy high-speed manoevering.
Maybe if you wanted WWI air combat
i spaaaaace on Venus then batteries would work fine, but if you wanted anything more aggressive than that (even WW2-style) you need nuclear power.
Nuclear jet engines are certainly possible. None have actually flown an aircraft, but a working nuclear reactor has certainly been run on a (large) aircraft by the US, and the USSR seems to have run similar tests.
This is the HTRE-3 test nuclear turbojet, minus a support structure. It did run, and could power up on reactor heat alone. It is pretty hefty though, and would have fitted in a bomber-sized aircraft, not a fighter.
It would be very difficult to miniaturize such an engine. Fission reactors are tricky to shrink, and there's a minimum mass of uranium required and a minimum mass of shielding so the rest of the aircraft (and the crew!) don't get cooked.
Supersonic nuclear ramjets were also developed as part of Project Pluto, with the Tory II-c model being actually run for several minutes.
(image source: Nuclear Powered Jet Engines: A Bad Idea that has Not Gone Away)
The problem with ramjets is that you need to get them up to speed somehow, so that the flow of air into the intake is sufficient to provide enough thrust to keep it flying. For going fast they'd certainly outperform a nuclear jet, but they won't run at lower speeds which probably harms their usefulness as in a fighter craft (as opposed to a missile).
In either case the biggest problem is finding some fissiles. Venus probably has similar reserves of Uranium to Earth, but good luck digging that stuff up. You'd have to import it, but then you'd have to import almost everything so it isn't the end of the world.
On the bright side, any catastrophic failures aren't going to be causing any environmental concerns, because you won't get much fallout above the clouds and no-one will be visiting the crash site in person.
If your tech level can swing to compact fusion plants, that might be better. Fusion might scale down better than fission, and there are fusion reactions that reduce the amount of seriously problematic radiation such as p+11B. Though often billed as "aneutronic", you'll still a small number of neutrons and some very nasty high-energy x-rays so you can't skip the radiation shielding.
You can use a fusion-to-electricity setup to drive jets or propellers, or a simpler and probably much more efficient heat-exchange system that uses fusion energy to heat incoming air in the same way that the HTRE-3 design did. There are even more exotic possibilities such as using direct energy conversion of high-velocity fusion products to drive a megavolt-level electron beam which could be used to heat up incoming air like a "normal" nuclear jet, or use any other solid propellant for a quick high-thrust boost (up to and potentially including operating as an SSTO rocket for space operations).