99% companies have been using Windows for the past 30 years. I would gladly accept any job using Windows, even more if they paid well. I hate Windows way more than everyone else, but being unemployed is worse nowadays.
I haven’t found a company that enforces windows of everyone. Seems ridiculous. I would sign the contract then simply require a Mac because I don’t know how to use Windows. IT be dammed.
Smaller companies, maybe. But bigger companies will have a ‘Security and Compliance’ department which will force everyone to use a company-supported platform. It goes beyond OS too. Unapproved apps, even if you are allowed to install them, may not connect to company resources.
for a senior engineer position though? That seems counterproductive. I would expect it of one of the entry levels or non-it but forcing a windows ecosystem on a development or engineering sector screams red flag to me.

A senior engineer obviously needs (and knows how to handle) considerably more access to their workstation and company IT infrastructure than the average employee. On the other hand, I’ve occasionally read complaints from IT security types about engineers being way too eager to install sketchy stuff.

There’s some truth to those complaints. I might need to try out several libraries and tools to see what works best for a certain use case. Is that new one with 15 stars on Github actually safe? Are all of its dependencies? How many developers perform a task like that in a sandbox? How many of those perform a thorough audit before taking it out of the sandbox?