I don't know anything about the quality of the Laowa adapter, but (if it's optically up to the task), what about the 17mm Canon TS-E on the Laowa and the GFX?
Alternatively, if you're willing to take the GFX out of the picture, there are a couple of solutions... Nikon has a 24mm PC-E lens (that's about due for an update - Nikon guru Thom Hogan likes the 19mm PC-E much better), and there's probably no better body for a tilt/shift lens than a Z7 (the FTZ adapter is really solid). I mention the Z7 instead of the D850 because of the fantastic full-time live view on the Z7. Tilting and shifting is one case where a magnifiable electronic view is far superior to a DSLR.
The Z7/D850 sensor is enough newer than the larger GFX 50 sensor that it's just about the same image quality. I own a Z7, and I looked very closely at output from it and the GFX (50R, but same IQ as the 50S) before choosing the Nikon. It's a real pixel-peep to tell the difference, and the size and weight of the Z7 won the day. Of course the question here is the GFX 100! The very best 24x36mm sensors have caught up to an older "small medium format" sensor, but the 100 MP sensor will almost certainly reestablish a lead for MF.
Canon, of course, has a 24mm TS-E. The next body in the EOS-R series is probably the one you want if you're using a GFX. Canon has a lot of things worked out really well on the EOS-R line (especially the lenses and adapters), but neither the R nor the RP has a class leading sensor. In your situation, I might either wait for whatever they're releasing this year at the top of the EOS-R line or pick up an EOS-RP to get used to how Canon mirrorless does things (you might lose a few hundred dollars selling the RP, but you got a start with the lens and whatever similarities there are in the body)...
There are two other options - one is the Canon 24mm lens on a Nikon or Sony body (the Canon may well be sharper than the Nikon lens, and is the more versatile, with tilt and shift both working on any axis) using an adapter. These lenses would be adapted on any mirrorless body since they are DSLR lenses - but the first-party adapters (Canon DSLR lens to Canon mirrorless body or Nikon lens to Nikon body) are likely to be less problematical than a cross-brand adapter.
The final option is that Fuji is reputed to be working on a native GFX tilt/shift lens... No solid dates on that one.
