Can I fit a compact cassette with a long cage derailleur?
Unlikely to cause any problems. A long cage R7000 (Shadow type) is rated for 28-34t cassettes. The short cage is rated for 25-30t, so going from 32t to 30t or 28t would be fine.
Expect to need to make normal adjustments for the new cassette, but it should work fine.
Of course it depends which precise RD you have, and since you didn't say I can't be 100% certain.