It is difficult to help without more information. But if you are entirely new to Linux you might be better off trying pop OS or Linux Mint. EOS is easy to install but arch based systems require knowledge or willingness to learn about package maintainance ideally. Seing that one problem leads you to hop back to windows, see you back later perhaps…
I suspect you either used an older iso, installed offline and updated, or installed eos on this computer a while back and have not been updating regularly. Arch is rolling release and requires more regular updates than other point release distro a like Pop OS.
For the grub issue, you just had to add the one command I posted above. It is a one time thing, and unlucky if it happened to you.
If you are stuck at reboot black screen…An easier option if you have your data backed up, is to download the latest iso and reinstall eos. Or seek support in the grub thread. People are really willing to help.