Trek DS3
 

Anyone know max tire size for these please ? It’s a 2019 model and has the 700 x 38 standard. Thanks

The 2020 (that looks to have the same frame, based on pictures) has a clearance for 2.1in without fenders, and 45mm with fenders.

Note that the 2020 DS3 also came with super narrow rims (17mm inside width, I don't remember exactly, but I suspect the 2019 should be similar), that can be limiting factor for wide tires. For references, there are several online charts that give the 'compatible' rim sizes for a given inside rim width. 35mm is often given as the limit between "recommended" and "supported" for rims with inside width of 17mm.

That being said, when I had the stock wheels, I was running 44mm tires (Schwalbe Smart Sam, good compromise between road and off-road), without issues. But 40mm tubeless with supple tires gives a much better ride on rough gravel than more rigid 44mm tires.