Thats a big question with a lot of potential answers. All I can do is offer some suggestions.
Unless you have a specific reason for only using one parition, going with at least three partitions (/boot, root (/), swap) is more ideal. The swap partition will allow you to hibernate and sleep your computer (you can't without it) and separate root and boot partitions will make repairs waaay easier down the line.
It also appears you are using MBR (dos) and BIOS. Unless your on old hardware that won't support it, using UEFI and GPT is usually preferred. Its the equivalent of old tech vs next gen.
Is secure boot enabled? Have you previously confirmed that the disk will boot Linux properly? Sometimes secure boot or another firmware setting will get in the way and need to be corrected since Arch doesn't sign itself automatically. Thats easy to fix, just take a look at your BIOS settings.
Installing arch can be a huge pain, but there is good news! The whole point of arch is too fail. Failing forces you to learn things you didn't previously know and become a more adept linux user. Good luck with your travels and welcome to the community.
edit: You also may want to try adding the boot flag to the partition via gdisk or parted.