We did the same. We normally have "office days" on Monday and Friday, for team meetings etc. and the other days are for everyone to decide what works for them. Most have one or two fixed WFH days.

Due to Covid-19 we changed it first to "optional WFH" (but with a hint that it may be a good idea) on all days, then "please WFH", and now "mandatory WFH, unless absolutely impossible"