I have a friend who ended up in exactly the same situation a year ago - her boss wanted to force everyone back to the office without putting anything in writing, so she asked for the changes to be documented in an email to have a paper trail. After two years of full remote work, it had basically become the standard for the job, so technically it was a unilateral change to the contract without agreement, which you can challenge.
Here's what she did: she documented everything (emails, dates), formally asked in writing whether this was a real contract modification or just a temporary directive, and mentioned that employee agreement was necessary for such a change. Her employer eventually offered a compromise - 2 days in the office - because they knew forcing it without solid justification risked damaging relationships or ending up in labor court. If you really want to push back, do the same thing: put everything in writing, ask the question clearly, and if you have other colleagues in the same boat you've got more leverage together.