To answer the original two-part question:
"...how many of [structural engineers] ... do so remotely, or are open to ... (having employees work remotely)?
A1: Solo practitioner. Fully remote since 2020.
A2: Not open to having remote employees with the exception of drafters, engineering reviewers, and/or pre-existing relationships with engineers (sometimes having developed these remotely via independent reviews).
Lots of new jobs are advertising a hybrid schedule of 3-4 days in the office and 1-2 days remote.
If I could turn back time, I would be absolutely all-in on these jobs (see below for my perspective on the effectiveness of water cooler talk). As a solo practitioner, I see more benefit in keeping on my own path rather than return to office work. Simply put, the cost of commuting + the extras (coffee, lunch, fixed 9-5 schedule, doggy daycare, kid pick-up/drop-off, appointments, comforts of home) outweighs the potential benefit of joining a firm's office even if that means somehow achieving structural engineering nirvana with a StructEng Yoda. The reality is that there are financial and health benefits (commuting ain't kind to colitis) with me working remotely and I am undoubtedly reaching closer to a my own level of satisfaction with structural engineering.
I have a lot of EIT's applying to my firm (me) probably because they do a buck-shot blast for every structural engineering firm in a 50km radius. Most of them are way to junior for me to guide remotely. I attempted this one time on a conditional basis, and it was like helping someone do their homework. No fault of their own. I think if I were to ever reconsider this I would need: (1) a full-time licensed partner to bring in additional work; (2) a full-time drafter to make everything consistent; (3) a documented training manual or system.
There are lots of good comments and perspectives from others above. There are suggestions that working in the office gets you more face time with your peers and mentors. I agree to an extent but know, from my experience, that this can be far from the truth in a smaller office. Having worked in small-ish firms my whole career (<12 engineers in a department) I always felt like the work punted onto my desk was done so haphazardly and with a "figure it out yourself" attitude. There were a small exception of really inspiring engineers, but mostly it was the same as remote work. Head down, pencil on paper until 5 o'clock.