I have the 20L and I’m certain from experience that it will not fit, but even the 30L will not fit the FW16 with the dgpu, according to the listed dimensions.
From peakdesign.com
Max Laptop Carry
40.6cm x 27.4cm x 3.8cm (16" x 10.8" x 1.5")
Fits 2021 Macbook Pro 14" and 16" models
Holds most 16” laptops
This fits the FW16 without the dgpu module, which which is 35.7cm x 27cm x 1.8cm.
But the dgpu dimensions make that 35.7cm x 29cm x 2.1cm, which is too wide for the 30L laptop compartment
Here’s the specs for the 20L:
MAX LAPTOP CARRY
38.1cm x 25.4cm x 2.5cm (15"x10"x1")
Holds 15/16” Macbook Pro
So you can see that either FW16 option is too wide for the 20L