Basically what @The_Red_Queen says above. This:
What about if the surprise attack works only for any character in stealth? First hidden character attacks, then non stealthed characters get brought into initiative like normal, any others in stealth get to make their surprise attack first then added to the initiative order.
seems basically the same as
We have suggested that all enemies and party members enter combat, roll for initiative and get slotted into the queue, then our initial character gets to complete any other actions and bonus actions (beyond their initial attack) before ending their turn. Any enemies would effectively skip their turns in this first round as they’re all surprised, so what actually happens in this first round is that the rest of our party get to take their actions and bonus actions, with the advantage of starting their turn in stealth as they were hidden when combat started. Our "surprising" character then gets to make their second attack, but by then enemies can take reactions and then combat proceeds as normal.
But the first suggestion means that players must manually bring each stealthed party member into initiative. This is needless work and in multiplayer, this means that any players in TB mode have to
wait even if it's their turn, otherwise they'll advance the turn order and enemies might be able to go before the stealthed characters make their surprise attacks to enter the initiative.
The main mechanical hurdle of the latter suggestion is making sure all enemies are Surprised for their first turn. But BG3 already does something like this, no? I've seen many reports that attacking from stealth leads to the PCs getting an entire turn or two before the enemies can go.
I just can't enjoy playing a game by announcing myself to the enemy, makes me feel like an idiot with no sense of tactics. Will take the messy system we have now over having the tactical ambush ability removed, even though it is far from ideal. I don't usually play TB games and not being able to set up characters for simultaneous actions is extremely frustrating, this is why I want proper pause and queued/ready action capability, the latter of which is already in DnD rules.
I really do think that what you want, in essence, is covered by the Surprised rules for 5e. It gives your party an entire turn to act before any** of the enemies can go.
**depending on the exact implementation Larian/the DM chooses: whether enemies automatically get a perception check once the first attack is made.
