Do you have a citation for this?
I'll offer a citation from the IRS that strongly suggests (though does not 100% prove) this is not the case:
"Can I set up a SEP for my self-employment income if I participate in my employer's retirement plan?
Yes, you can set up a SEP for your self-employed business even if you participate in your employer's retirement plan at a second job."
That suggests that you can contribute to a SEP even if you yourself are participating in a 401K, let alone if your spouse is merely offered one.
[0] https://www.irs.gov/retirement-plans/retirement-plans-faqs-r...
https://www.irs.gov/publications/p560#en_US_2019_publink1000...
It seems only people who are employed by employers that don't offer 401k get screwed if the spouse does have a 401k and you're over certain incomes:
Not if your spouse works for an employer that offers a 401k.