Use
Mechanic, Ability, Roleplay, Quality of Life


How
To sit, sneak, look directly down, right click the blinking prompt and release sneak.
Only works when you release crouch as it kicks you from seat.
The prompt will only show when the conditions are met and the area you are wanting to sit is available.

Kept it intuitively simple

Details
Multiplayer friendly.
Survival mode friendly.

It uses interaction & snowball entities, functions, tags, and scoreboard. Pack is efficient only using under 30 commands
This is exclusively for Minecraft Java Version 1.21 as it has more supported features that prevent total failure.

Commands
Run command for similar info to here /function .help:sit/info
Run command for uninstallation /function .help:sit/uninstall
Run optional command to sit /trigger sit


Enjoy!
I am sorry for earlier versions as minecraft has limitations to datapacks, with the current 1.21 it gives more flexibility of possibilites in a datapack and I totally revamped it's functions from scratch.

Other than that enjoy this simply vanilla sit datapack.