My OPT already ended and I was in the 60-day F-1 grace period when my employer filed a cap-subject H-1B change of status. Does cap-gap let me work again?

No. A qualifying cap-gap filing can extend your F-1 status during the gap, but if your OPT work authorization had already ended when the H-1B petition was filed, there is no employment authorization to extend. You can remain in status under the cap-gap rules if you qualify, but you cannot restart work just because of the cap-gap.