TWRP for Pixel 3 XL on Android 10 or 11 DOES NOT WORK!
This is an issue where TWRP team has not given a solution yet they keep posting their TWRP as if it worked for Pixel 3 XL. Probably issue with Pixel 3 also.
Now, a lot of their TWRP builds are made automatic so there’s no human verification and that’s why and I don’t blame them. But you might want to KNOW that TWRP does not work on Android 10 or 11 as even “fastboot boot twrp.img” will simply give you an error. So if you want TWRP on your Pixel 3 XL so you can install cusotm ROMs, just re-install latest Android 9 to get it working.
UPDATE: Just confirmed TWRP works FINE on Android 9.0 after downgrading.