I have a theory if you’ve checked the clutch slave and it appears to be moving normally.
Water got in to the clutch disk and didn’t dry before you parked it, rust formed over night, the clutch and flywheel are now stuck together just enough that pushing the clutch pedal isn’t seperating them.
Before tearing it all apart, you may want to try getting the car started in first gear (maybe have someone push it at the same time you’re trying this), get up some speed, and hit the brakes and gas at the same time trying to make the clutch slip. See if that snaps it loose.