The Google Pixel 9a generally supports OEM unlocking, provided it is a device purchased directly from Google or an independent retailer and not a carrier variant with a locked bootloader. In the developer options, you will find the option "OEM unlock", which you must activate to unlock the bootloader. Note that unlocking the bootloader deletes all data on the device and some Google functions, especially in the AI area, may no longer be available afterwards.

I do not currently have official confirmation from Google itself, but the common practice for Pixel devices is that bootloader unlocking is possible for free models. The option may be disabled on devices from certain mobile phone providers (e.g. Verizon, AT&T, T-Mobile).

If you have a device purchased directly from Google or an independent retailer, you can usually unlock the bootloader. If you are unsure, it is advisable to ask the retailer whether it is an unlocked model before purchasing.