cbrngrz An unrelated question, I've just found out about this OS and was wondering if I could just buy an unlocked phone from a retailer (like best buy or something) and install the OS without having to do anything extra? Or is that not the same "unlocked" that is needed?
For this, read through the Web installer page. It has everything you need to know (do feel free to ask more questions if there is anything you are unclear about though).
But the part you're asking about is:
Enabling OEM unlocking
OEM unlocking needs to be enabled from within the operating system.
Enable the developer options menu by going to Settings > About phone/tablet and repeatedly pressing the Build number menu entry until developer mode is enabled.
Next, go to Settings > System > Developer options and toggle on the OEM unlocking setting. On device model variants (SKUs) which support being sold as locked devices by carriers, enabling OEM unlocking requires internet access so that the stock OS can check if the device was sold as locked by a carrier.
For the Pixel 6a, OEM unlocking won't work with the version of the stock OS from the factory. You need to update it to the June 2022 release or later via an over-the-air update. After you've updated it you'll also need to factory reset the device to fix OEM unlocking.