A forced (mandatory) update means the new version fixes something everyone needs, so SyncNow applies it before continuing.
Most updates are optional and just keep you current. Occasionally a release is flagged as mandatory, usually because it carries an important fix, a security improvement, or a change required to stay compatible with the cloud. In that case SyncNow does not let you keep running the old build. It downloads the new version, verifies it with SHA-256, applies it, and restarts on the updated version.
What you need to do
Nothing special. Just let it finish, which usually takes only a moment. The same safeguards apply as with any update: the file is checksum-verified before it runs, an anti-loop guard prevents restart cycles, and SyncNow can roll back if needed. A forced update is closely tied to the minimum supported version: if your build falls below that line, moving up is treated as required too. It is simply the system making sure no one is left on a build that should no longer be in use.