FYI: You can enable them in Gnome with Gnome-Tweaks. Apparently a very recent version of Gnome dropped this functionality for reasons that are beyond my understanding (but that's often the case when I look at the decisions that the Gnome devs make).

However, getting the Control -> Command/Super thing to work is much trickier. The best way is to use this: https://github.com/mooz/xkeysnail

However when I tried that, I ran into all kinds of weird behaviours all over the OS. Also, it doesn't work with Wayland.

Another option is https://kinto.sh . It worked perfectly for me out of the box on Pop OS, and with a few tweaks to shortcuts I’m pretty happy with the experience to the point where I can fairly seamlessly switch between computers and not be driven crazy by the shortcuts.