games are about fun, if something only adds realism for no reason it's not good game design to add it
- adding various types of radiators (solid, droplet, etc.), gloving when weapons fire or engines activate, shooting them off prevents system from running
- planets on eccentric orbits with wildly varying surface conditions in mere days as the planet periodically get closer and farther to the star, from frozen solid to metals flowing like water days apart
- aerostat habitats in the atmosphere on gas giants or Venus like worlds, you could fly around but go to low (or get swept by a storm) and you might get crushed
- radiation belts, sun grazing comets or energy harvesting stations very close to a stellar body, can enter for a very limited time until even your shielded systems burn out - and good like with repair space walks!
- tidally locked bodies, where one side is always illuminated and the other one has an eternal night, with perhaps a thin habitable belt where conditions are just right for life, presenting interesting options for story telling and world building
And even that solution is only temporary. Its possible to watch the simulation go on so long that planets begin to de-orbit the sun as the math simulation breaks down. For spoiler reasons players don't run into this issue, but it exists.
PS: If you haven't played Outer Wilds and you enjoy exploration/puzzle games go play it. Avoid spoilers if possible.
Players can FTL, but big stuff (planets, stations) orbit realistically.
FTL only via gates or jump points, other flight only via realistic newtonian physics.
No FTL/no intra syste FTL (kinda like in Webers Honorverse SF series).
This third option limits playable areas for multiplayer games to a solar system or even a section of it (cislunar space or a gas giant + moons). And even with very advanced engines flights would still take hours or days. On the other hand this would present an interesting mechnics - once you do a burn, you know when you will arrive at your destination or encounter an enemy that already committed to a trajectory.
Then you join for the battle (or setup a battle program beforehand) before doing another burn (if you survive) & signing off again while the ship continues flying the trajectory.
Kinda like correspondence chess with hectic minutes of nuclear space ships trying to kill each other during encounters.