CrazyDiamond I was using a Pixel 6a to test this.
I can't tell from the description what could be wrong. You could try connecting a different mouse. You can also connect a wired keyboard and use it to navigate the menus with Tab, Space and Enter. I tested this right now. When you've finished the setup wizard and are at the home screen, press the Up button and use the other arrow keys to select the Settings app. When you are in the Settings app, search for "build number", hit Enter twice to navigate to it, then mash Enter until you can unlock Developer options. Then, in the Settings app, do a search for "developer options" so you can enter that menu.* Then enable OEM Unlocking.
Small note: I'm noticing that when selecting the 'Next' button in the setup wizard by using Tab, it's barely highlighted, so you'll have to look carefully. Just press Tab again and again until you see that the correct stuff is selected.
*When I tried to go directly to the Developers options menu, it would not open when I pressed Enter. But doing a manual search for it worked.