Edit to my comment: Based on the answers below there seems to be confusion about employment contracts. Signing a letter that specifies your position and salary, as well as NDA forms, are all contracts, but not employment contracts in the traditional sense I meant here.

Traditional employment contracts, which were common years ago but are now used principally for C-suite positions, typically have terms employees can sue to enforce such as WFH.

For most positions in tech, nothing in the paperwork will give you a way of enforcing WFH if the company changes its policies.

That's what I meant by my comment above, which I can no longer edit. (I should have been clearer.)