If you could click one button on a website and override your entire OS, malware makers would have a field day with it.
Such things sound cool but are untenable in the real world. Microsoft used to have downloadable binaries on websites (ActiveX) and that showed what a stupid idea it was :) There's a reason internet explorer has such a bad name.
You have to grant webUSB permission and enable OEM unlocking on your Pixel, but GrapheneOS can be installed from a website: https://grapheneos.org/install/web
It is arguably easier than installing windows on a laptop (if you were someone who had done neither before), since it is just a few buttons to press.
Such things sound cool but are untenable in the real world. Microsoft used to have downloadable binaries on websites (ActiveX) and that showed what a stupid idea it was :) There's a reason internet explorer has such a bad name.