Are there professional degrees like that for, say, mathematics or physics?

An aside, the Actuarial profession's fellowship credentials (FSA/FCAS) are considered to be roughly equivalent in content to a professional doctorate (not counting a medical residency), and have a completely different format.

It's mostly exam based from pure self study, and aspiring actuaries typically work full time in the industry after passing the first 2-3 exams and finishing a bachelor's (which can be in any subject). Typical travel time from the first exam to the fellowship credential is 6-8 years, IIRC. Employers pay employees for some study time and for exam leave for each exam, with a bonus for each one passed.

I bring this all up because there are a lot of other ways for education to be structured outside of the BS -> MS -> PhD pathway, and there are ways for learning to be integrated with industry.