If I could go back in time and change what courses I took for my CS degree, it would be the exact opposite.

I wish I'd gone more into theoretical computer science, quantum computing, cryptography, and in general just hard math and proofs.

I took a few such courses and some things have genuinely been useful to know about at work but were also mind-expanding new concepts. I would never ever have picked up those on the job.

Not to say the practical stuff hasn't been useful too (it has) but I feel confident I could pick up a new language easily anytime. Not so sure about formal proofs.