It is available in Settings under Accessibility\Seeing\Reduce Animation

If you check the enable-animations value you can see it toggles between true and false when you enable/disable the Reduce animation setting.

Can't you add the settings and submit a PR?

Not picking on you, as it seems this is common: treating open source software as if it's someone's else's product, and treating ourselves as helpless consumers.

IIRC Gnome is one of those projects where it can be VERY difficult to get a PR submitted because the developers have Opinions.

Even if the PR is accepted, in a couple years they'll throw everything away again and the option will be gone

Instead of being sarcasting and unhelpful, you all could have a look at a settings window and realize that the option already exist and there is no PR to do.

I'm not being sarcastic. They've had 3 "waves" where they either threw away a whole bunch of stuff or outright started from scratch. Not to mention the ever changing libraries (there is no stability). I'm obviously not talking about this one feature, but with a history like that, why expend the effort, there's basically no guarantee how long your contribution is going to last.

Not that easy, not everyone knows how to code. Also, even if you still need to find/add what you need in a presumably massive codebase.

I'm not saying it's easy or that everyone is capable. Only that it CAN be changed, but the conversations around OSS often don't reflect that reality. (We've all seen Github issues being abused as a support channel, often with a strong odor of entitlement)

If someone has strong feelings about how a UI is lacking, why suppress it in order to be more polite and avoid appearing entitled? That's a very useful signal. Imagine if nobody expressed their strongly-held opinions about UIs; nobody would know what's missing or bad. Why must everyone who complains about something also attempt to fix it themselves?

Unless you're willing to commit the effort and resources necessary to fork, it is someone else's product.

you are not wrong, I could. But it is there I read further in the comments. I've seen this in Gnome in the past though too, or settings disappear.

You can use dconf Editor to search and change all available settings for Gnome, GTK apps and shell extensions.

It also shows you the gsettings key so you can easily shove everything into a script if you want.