I have worked in a mostly remote company. Eventually everyone just stops going to the office as they are not sure if anyone will be there. Eventually the real estate sits empty and the employer exits it
You can have a company with many offices, and every employee in an office all the time, but no one office designated as the HQ.
Doesn't happen in our company.
I worked mostly remote and we met up every Wednesday - unless we had reasons to move it to another day (client meeting, conference, etc).
It worked out really well since everybody came together at the same time.