It seems that a lot of things are just no possible to learn on the side as well. For example, doing anything at a large scale. That could be HPC stuff or just designing and building systems that need to handle high throughput without slowing or failing. I can’t afford to have the sort of projects that would allow me to learn those things.
The exception I can imagine is working on high visibility OSS projects and is a huge time sink and might as well be a second job.
Also, you’d be surprised how much you can get done on a modern PC with vms or containers, it isn’t the nineties or aughts any longer. We used to run a full vfx company on what amounts to a single souped $10k PC today.
Or, rent a heavy-duty cloud vm for $100 a month, small investment but clock ticking will get you motivated.