That would effectively mean increasing salary of the current employees that choose to go to the office by 20%. Alternatively, that'd mean reducing salary of current employees that choose not to.
Either way, that seems like a horribly inefficient way to deal with the problem. Most companies choose much more subtle approaches, such as:
0) Stop hiring remote -> build a new workforce that does not expect remote conditions
1) Mandate RTO (just like Meta, Amazon, Google, Apple, and others did)
2) Start putting people who do not respect RTO on PIP, or on some other bullshit process that'll threaten to fire those that do not conform while giving you, the company, enough time to replace them with new hires.
3) Slowly and silently follow through 2) until remote is a thing for <10-15% of the workforce.
This gives the company a number of advantages, such as:
1) Not appearing evil
2) Not dealing with disruptions caused by mass employee exit
Companies that really want RTO don't have to do it in a "big bang" way. Such companies would rather do it silently while telling you how they value your opinions on what the future workplace policy should be.
They'll get away with it IIF point 0 is possible. I hope it is not, but who knows.