Thank you very much! The EFI folder worked, and I was able to install Big Sur on an external SSD and an internal SSD. Both are SK Hynix (brand) 512GB NVMe, internal is the #BC511 model, external is the #BC711 model. Both run MacOS, but BC711 (external) runs MacOS fast! The internal BC511 runs slowly, taking about 24 bounces to open apps. Also the wifi doesn't work with the default Intel model AX201NGW, I have an Apple approved WLAN model BCM94360NG but it works very slowly, barely 1mbps download speed. I'll keep playing it and see if I can find updated kexts that will fix the wifi. I also purchased a USBC ethernet adapter identified by macOS but which keeps auto-assigning an IP without internet. I could just keep MacOS on the external USBC SSD since it runs fast, but that defeats the purpose of having it on a laptop.
Thanks again and sorry for my Italian, I'm using google translator. 🙂