The hand requirement of weapons in 5e is only concerned with the business moment of the weapon's use - a two-handed weapon it doesn't mean you have to have both hands on the object all the time; you can hold a greatsword in one hand without putting it away, while you use your other hand for the somatic components of a bonus action spell, and then hit something with your two-handed sword, two-handed, without having had to sheath or draw anything... that's perfectly fine. The same is true of things like crossbows. In the case of hand-crossbows, being one-handed only means that you can aim and fire it (the important part) with one hand, while your other hand is full - it's not saying that you also load and reset it with one hand. Relatedly, loading and resetting a crossbow doesn't take up any part of your turn - it's presumed to be a part of the action you take and possibly the other minor free activity that takes place on your turn.
A big problem that it seems unlikely Larian will ever fix is that you should absolutely be able to wield a hand crossbow in one hand and a shield in the other, if you want to. Their system doesn't allow this currently because they've made a hard distinction between melee and ranged weapon sets; you can't have a one-handed ranged weapon and a shield out at the same time. Relatedly, their system also can't cope with weapons with the thrown property (javelins, hand-axes etc.).
As an aside...
When I first played I had the same experience. I wasn't really familiar with how different 5E was from 3.5 etc. It wasn't until I started playing with other people that I realized all the mistakes I was making.
[...]
1) If you have 16 str you can throw most medium sized monsters into other monsters with no ability check and it does massive damage (you can kill all the Cambions on the ship this way)
2) You get shove as a bonus action instead of a full action which is super OP as you can shove people off cliffs and then attack.
3) You can throw potions next to people to heal them.
[...]
5) Barrelmancy - you can put an explosive barrel anywhere and nobody notices. Or you can stack crates within crates to make a massive heavy object that you can throw at people for a ton of damage.
6) You can drop a candle from your inventory and use it to light your entire weapon on fire as a bonus dip action...from a candle.
I know you probably didn't intend it this way, but please don't do D&d, or 5e the extremely besmirching disservice of conflating any of this with 5e or D&D in general... This is all BG3's game-breaking homebrew, and nothing to do with 5e.
