I’m unable to assign F4 to a hotkey in the game. Can you help me figure whether it’s my computer that’s faulty or if it’s a problem inside the game?
I’m sorry if this is the wrong forum.
I just tried this in-game and was able to reassing F4 to something else. By default (I think) it is assigned to target party member. No clue if modifiers work with F-keys but you should not try to bind alt+f4 
Can you bind other F-keys? If not then problem is likely somewhere else. Eg. some addon could be interfering, some laptops and keyboards have FN-key which is used to switch between normal F-keys and special function keys (eg. volume controls) so I would check that, too.
All my other F-keys work.
F4 is certainly a valid Keybind and you should be able to use it in game. If you are unable to use the key, it’s more likely the the key input is being stolen by another application such as an overlay. It could be worthwhile closing as many background applications as possible.
As Greller said, It is possible that certain keyboards may block this key from being used in game via game mode settings or while a function is assigned (mostly laptop keyboards).