DLSS 5 stays on between launches on the OptiScaler engine. OptiScaler ships neural rendering off ([DlssNr] Enabled defaults to false), and its overlay toggle lives only in memory unless you find the Save button — so the whole point of the install had to be switched back on every time the game started. Install now writes [DlssNr] Enabled=true itself.
If you already have it installed, run Install again on that game, or set Enabled=true under [DlssNr] in OptiScaler.ini by hand. That key is section-scoped: Enabled appears under half a dozen headings in that file, and only the one under [DlssNr] is the right one.