The stripe is the cathode, which is negative side. But it depends how you look at it. For a flyback diode wiring configuration, we are going to put the negative side of the diode on the positive power supply going to the solenoid, relay coil, or clutch. The anode or positive side of the diode is connected to ground. It won't conduct electricity until the switch is opened and the magnetic field of the coil collapses. Then it will conduct to discharge the coil and prevent an arc across the opened switch contacts. Here's a good article about it.
https://www.electronicshub.org/flyba...heeling-diode/