I cant speak for engineers, but as a mathematician I wholeheartedly disagree with everything you claim in your comment. Almost none of the mathematicians that I know care about the optimization aspect of mathematics: the pursuit of optemizing constants in theorems and providing minor technical improvements is mostly seen as pointless unless there are significant new mathematical insights that fuel the improvement. I think most mathematicians rather build their identity around providing actual understanding of problems using mathematics and improving society's understanding of mathematical problems.
Of course AI threatens this too, but the threat is of a much lesser degree. One could even argue that AI is helpful here with getting mathematicians to the 'frontier of knowledge' as AI is usually good in combining ideas from different fields.
I would like to learn more about Web development and related knowledge (networking, security). Currently my programming knowledge is primarily system languages+python. I'm thinking of building a few websites / apps from scratch, and perhaps hosting my own server. Recommendations for frameworks or do's/don'ts are very welcome.
Second thing is networking skills at my (future) job.
One thing I regret from my PhD is not seeking collaborators out more actively and building my network. Although I'm moving to industry, I've realised that having a strong professional network is vital for job security and can make the job much easier and more fun.