I have had the exact same issue also from BestBuy within the past month.
Carrier unlocked and bootloader unlockable are completely different things. Unfortunately phones advertised as "Unlocked" or even "Fully Unlocked" are usually only guranteeing the former, with the latter being up to chance. "Factory Unlocked" should mean the bootloader is unlockable, but it's not infrequent for phones to be misadvertised.
Atm your phone's bootloader is not unlockable. The above posts are correct that it may be possible to get the bootloader unlocked, however you should first check to see if it's a Verizon model so that you don't waste your time.
Verizon models have their bootloader permanently locked, and Verizon will not unlock it. If it is a Verizon model then you are SOL. It sucks. If I may indulge in some relativley tame and well deserved ad hominem, it's a very environmentally and consumer hostile company.
To check, type your IMEI into Google's Repair page. It will show like "Pixel 8 (Verizon)" if it's Verizon.
If it's not Verizon then try the advice above and search around, some people have had luck getting other models unlocked.
In my case I kept the Verizon model for a bit and just ordered and returned new phones until I got one with an unlockable bootloader and then sold the Verizon model. Most people only care that it's carrier unlocked so it's not hard to more or less break even pricewise, but it takes time and is a pain. I have yet to find a single vendor who will just gurantee me an unlocked phone even after reaching for support and providing very simple instructions for verifying.