The community has no obligation to help people. This site is a discussion forum, not a "help community", but there are very nice and knowledgeable people on here who help others with issues/questions who ask for nothing in return. We're not tech support.
Pixel 3XL is end of life. No software or security updates regardless of whether you use Stock Android or GrapheneOS. You might consider using a newer phone, like Pixel 6 or 7.
The reason you didn't get any responses is because it sounds like you did everything right. Others who've had issues when they did everything right have causes that are hard to determine...
Double/triple check prerequisites: https://grapheneos.org/install/web#prerequisites especially the parts about cables and ports.
Don't use any cable other than the one that came with the phone. Don't use adapters to switch from USB-C to something else.
If that fails, try another browser, or different computer, or try to flash from a separate phone.
And if you do get GrapheneOS installed and haven't already left for good after your rude comment, I'd hope you will stick around and contribute to the community and help us help others who run into problems with their GrapheneOS installation.