Next steps after CS bachelor – more math, ML, or physics?

Work on developing professional / non-academic connections. aka ACM, IEEE, local 'clubs/organizations', relevant open source projects. This provides broader exposure to those looking to hire while also building one's credentials / show casing what interested in applying degree to. Demonstrates knowledge of how to use academic credentials outside of academic setting.

Insite: Everything else being equal, is someone one knows/familiar with someone's work more or less likely to hire an unknown or someone who's work/project(s) is familiar/known.

I went the reverse getting a BS in Physics and getting serious experience in aerospace. Later the computer science skills developed and I did get a MS in Operations Research. My last job before retirement was a serious data science/data engineer position and the US west coast salary was great (1 day job offer, top salary). I thought so much of data science had gotten dumbed down and was easily performed my anyone w basic ML skills. In my role, the physics was a great differentiator in understanding the nuances of more complex problems we were working on. This was issues related to optics, electro magnetics, three dimensional movements, etc. so, I seemed to end up directing a whole bunch of data scientists on various efforts. With the current situation in the US, I suspect there will be more defense work in the European countries, so I’d embrace something like a physics degree if you could find the opportunity.