on this website it is stated that a 60mm beach racing tyre (narrowly) fits, so perhaps a 55mm gravel tire is viable!
https://www.gravelbike.be/gravelbikes/tavelo-grow

Launched "soon" apparently, whatever that means🤷‍♂️
https://tavelo.cc/products/tavelo-grow
55f and 50r.

Anyone build one of these up yet?

Ide Schelling showed it with a 2.2" rear and 2.4" front, though not with any super wide gravel rims.

https://www.instagram.com/ideschelling/reel/DYo0yUHgTYR/

Front clearance looks great.

However, it's a bit hard to see what the actual clearance is on the rear. He doesn't show it from the top.
Officially, the rear takes 50mm measured. He says the 2.2" Ikon measures 54mm (i.e. less than 2.2") with relatively narrow rims, and it looks tight, but I'm not sure.
The 2.1" Thunder Burt on an XPLR-type rim (also ~54mm measured) is becoming a common racing setup, but I'm not sure I'd run it on the Tavelo Grow.