If you’re using flexible flat panels, you may be able to get away with a two sided eternabond tape, or something like a 2” wide Dicor roofing tape, but once down, that’s not coming off. THe Roof would also need to be prepped really good. WIth it not coming off, that to me is the same as drilling in the roof. I would not trust this adhesive alone to mount a flat panel. I think a squall could still take that flat panel off the roof. The flat panels need a space for air circulation underneath. Even with a flexible panel, the life of those is much shorter than a regular monocrystalline or polycrystalline panel.
I think my flat panel frames are aluminum, so magnets would not stick to those. Perhaps if you secured them somehow, it may stick to the roof. I may trust the Neodynum magnets, but I don’t know how long those will last. Some of those re so strong they may rip from the mount, or warp the roof if pulled off.