What do you think about a “Software Development and Security” degree?

This sounds like Software Security. It's a discipline of information security which covers security and its relation to software and the development that produces it –from minute details such as [1], through abstractions like [2] to architectural [3].

Our infosec tutors regretted that this wasn't mandatory reading for the code-focused computer scientists. Mostly infosec-oriented peers took the subject, who might need it the least.

Security should definitely be promoted with development.

[1]: https://www.cis.upenn.edu/~sga001/classes/cis331f19/resource...

[2]: https://owasp.org/Top10/A07_2021-Identification_and_Authenti...

[3]: https://owasp.org/Top10/A04_2021-Insecure_Design/

I think the field changes too fast for a vocational curriculum to make more sense then a general CS curriculum, at least for full 4-year degrees. If you are looking for vocational training/validation, then a certificate of some kind makes more sense. After all, if you aren't in it for the academic education, you probably don't want to spend 4 years on it, anyway.

Depends from which institution.

What type of degree?