I ordered a slightly used Pixel 3 xl from Amazon. When checking the warranty status it says it's the Tmobile version even though it's supposed to be the unlocked one. Will it work on all carriers?
It should work. You can check by going to one of the MVNO websites that has an IMEI checker to see if the phone will work on their network. Try one for each main provider, Verizon, TMo, and ATT. I know Mint Mobile has one for TMo towers.
Verizon may be a little difficult as they are much more restrictive on unlocked phone compatibility (doesn't necessarily mean the phone is locked if they say it's not compatible) than the GSM networks. It's a safe bet to assume the phone is SIM unlocked if it works on both ATT and TMo networks.
99% certain that they will work on Verizon, but from my experience, activating them could be problematic. You may need to involve Tech Support to get the phone activated. Something about the IMEI needing to be "registered" on Verizon. There are many phones, og Pixel in my case, that work perfectly on Verizon when an already activated SIM is transferred, but they can't be easily directly activated.