Catch up Impossible

yeah, wish i knew too. I feel like it's the way games are recorded in spring rts

in other words: no. unfortunately this is a build-in feature.

you "could" maxzoom in to a place with no action and also disable luaui and re-enable when you are at the specific timecode. this saves both calculating power and should speed up the simulation

type ingame in chat
/luaui disable
/luiaui enable

=> could this be done by default or a button?

Catching up should be mostly CPU bound I think and a lot of stuff will run single threaded. CPUs has basically stopped increasing the clock speed because it has diminishing returns compared to adding more cores on the CPU.
I think it is rare that Spring uses more than 8 GB of RAM so I'm not sure having more than 16 GB RAM helps unless you have a lot of other applications running.
Closing the browser can surely help since those tend to hog up all the RAM they can get their hands on. :-P

The game engine needs to fast-forward from the beginning to reach the present. Making checkpoints would be a solution, but it's really hard. That's because it would need to save every tiny detail exactly, or your version of the match could end up different from everyone else’s. For the Spring engine devs, I imagine the difficulty comes from how to account for every little detail, without breaking the game, or making the game simpler just to achieve this

How hard would it be to atleast introduce open coop games, where people can join after the game has been started. Start with or without a new commander where otherwise other people share units to the newly joined player.