The Travel Tripod is indeed compatible with most Arca-compatible plates and L-brackets.
How? The ball head's removable pins allow longer plates and L-brackets to lock in place.
While Arca is the closest thing there is to a standard tripod plate geometry since about 85% of professional tripods use it, we just say "most" and not "all". We've learned over the years that there can be slight geometric variance across brands.
Still, we really should say "a vast majority" because we have yet to find an Arca-compatible plate that does not work with the Travel Tripod. If you do, be sure to let us know at firstname.lastname@example.org!
In the meantime, here's a list of third-party plates/L-brackets that we've confirmed to be compatible with our PD Travel Tripod:
1. 3 Legged Thing QR11-L
2. Universal Camera L Bracket Quick Release L Plate 1/4" Screw Arca Swiss Vertical Video Shooting (Compatible with Manfrotto, Nikon D750, D850, D3400, Canon 80D, 5D, 7D, Sony a7riii, a6000, a6500, DSLR Tripod Head)
3. 3 Legged Thing QR11-LG Universal L-Bracket - Slate (Grey)
4. Really Right Stuff Ultralight L-Plate for Nikon D850
5. Really Right Stuff L-Plate Set for Sony Alpha a9 and a7R III
6. Really Right Stuff Ultralight L-Bracket for Nikon Z 7 and Z 6
7. Really Right Stuff B5DMkIV-L Set L-Plate for Canon 5D Mark IV
8. Kirk BL-Z L-Bracket for Nikon Z7 And Z6
11. Gitzo plate
12. SIRUI plate