Stronghold is downloaded but it doesn´t open. My mac restarts and thats it. No Stronghold...

Are you using Catalina? From the game page:

Is there a work around for this? This is the only game I play on gog and it doesn't work on Mac anymore.

Without using a virtual machine/Wine for the Windows version or using Windows itself, no.

same here:

both, stronghold hd and stronghold crusader, don't work on my Mac anymore, even though they were working fine when I played it last time. restart, reinstallation of both galaxy and games, didn't solve the issue. it will also lead to a shutdown of gog.com while other games work well via galaxy.

Mac OS Big Sur 11

Is there any news on when they'll update Stronghold and Stronghold:Crusader for 64 bit Macs?

Same boat here.

Very annoying.

Look.
The biggest mistake you've made with buying a Mac is expecting them to work with or for you. That's simply not how it goes.

And given that Mac OS these days is simply Darwin based BSD with a bit of proprietary flair [UNIX], you're really not getting anything for your 1k$.

Even if a 64 bit update was made for these old titles, there's not a guarantee, (and in fact, I feel it would be surprising if) that Rosetta or similar translating software will be given continued support. With macos, it's their way, or the highway.