Actually, I found my own answer. The rule seems to have gone into effect in 2021 and it's in the "What's New for 2021" section of the 590a. I also found previous years publications on the IRS website and I do not see this rule about being covered by a workplace plan with respect to Roth IRAs (only traditional IRAs).
Links:
2021 590a: https://www.irs.gov/pub/irs-prior/p590a--2021.pdf
2020 590a: https://www.irs.gov/pub/irs-prior/p590a--2020.pdf
