I dm for groups and play in a few. Combat can be quick and sweet if everyone at the table knows the bloody rules and its muddy and slow in groups that dont. .
After nearly three years of alternate weekend games, our current group (stood down at present) has picked the rules up well enough that combats go quickly and smoothly. We do, however, have a girl who still forgets what die to roll and how much damage she is meant to be inflicting with a longbow. The round inevitably stalls when it reaches her, and she rarely has anything planned for her turn. It is frustrating. Luckily we are a fairly mature and well-balanced group so nobody has yet stood up and told her that she is an anchor around the group's neck. She's a lovely person, but my gods it is frustrating to play RPGs with her.
One of the groups that I play with also has a player like that with a simular problem but its her first ttrpg and we havent been playing for even a year yet. We also play abit unregulary so that isent helping either. If shes still doing it after 3 years though il start to ask questions xD
One of my players that I DM for is a poor planner as well. He only starts to think about his actions until its his turn, and then often reads the spells description rather then the spell itself. It infuriates the other players (and myself) but hes also autistic so I dont think to much of it. Luckily he generally is only slow the first 1 or 2 turns of combat in a session and then knows what the wants to do.
Point is, if you at least put some effort into understanding the rules AT ALL its not hard to make combat go faster. When other players or enemy monsters are taking their turns, think what you want to do. Unless you suddenly go down or something happens in the action right before yours you probably wont have to change your plan. The OP just saying 'combat is garbage' without taking a look why it is garbage to you is not a very helpfull stance and makes you look like you just dont like the system. 5th ed is very streamlined, if youve played 1 character for any length of time and know how your damage is calculated you know it for other classes as well, just that they use a different statline.
Bg3 does explain things poorly and if you dont have tabletlop knowledge I can understand things beeing confusing.
