KalTa289 Said:
"Can't really install Big Sur: I was trying to update and things kept going wrong, I ended up formatting the entire disk and now I'm trying to install a new one. Also I don't really have a USB flash drive, and it will take days even if I ordered it now."
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Get a New Flash Drive:
If you were to get a flash drive, get a new one. Do not get a preconfigured one, as it may have malware and such. So, as someone (i.e. friend) if you may format their USB Flash Drive for your own use (making sure they get all over their data off of it).
Ethernet:
Though you don't want to hear about Ethernet, here is the adapter to use: Belkin USB-C to Gigabit Ethernet Adapter - Apple
Ask for WiFi:
Go to a location where there is a stinger signal. If an available option, use a range extender to amplify the signal.