While SG is rolling out the new version, people who have attacked you ar some point in the recent past but are now upgraded to v22.1 won’t be revengeable until you upgrade to v22.1 too, at which point you can revenge as normal.
Once you upgrade, you will not be able to take revenge on people who are on v22 until they upgrade. So you’ll want to do all your revenges before upgrading.
Please note that the server won’t realize you have upgraded until you actually log in with the new version! So if you upgrade but then stay logged out for several hours, people on the old version will be able to attack you, but you won’t be able to revenge them once you finally log in on the new version.