The PL mount dates back to film cameras with Reflex lenses.Depending on how you define 'mirrorless lenses', their cine lenses feature PL mount versions and their broadcast lenses feature the B4 mount. For photo centric mirrorless lenses, Canon only does EF-M and RF versions.
B4 is harder to call.
B4 cameras did have pentaprism at the beginning so even if those cameras did not have a mirror the lenses technically could have been used on SLR cameras.
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