There is a thread with a Pixel 7a user who reports a similar problem, but I have a lot of Pixel install experience and have never faced an actual “hardware bricked” situation.
I do suspect that it had Android 16 on it before installing, which would lead to this install issue, but it could have been a problem with a USB connection or other problem as well, so it is all just speculation until you can get it back to working to try again.
Now to the problem, if the screen is active when connecting to a PC (you say it boots to Google recovery?), then you should be able to use flash.android.com from a Chromium-based browser to reflash Android 15 (using the dropdown to choose older builds or something like that until you find the Android 15 option). You do not need to re-lock the bootloader at the end of that process but it isn’t terrible if you do, you can just unlock again with fastboot flashing unlock.