Hello there and welcome, @eoifj!
It sounds like your phone is not in the bootloader interface, which is why it's not being detected.
Please join our Matrix room so that we can assist you with the installation in real-time. We find it's best for installation support rather than the asynchronous nature of the forum.
You can find links to join our Matrix community here:
https://grapheneos.org/contact#community
You can find my Matrix ID in my forum bio. Feel free to ping me when you're there and I'll be happy to walk you through it!