Welcome to the forum! 
Yes, you do. 
You should leave it disabled. There is a way to get Manjaro to work with Secure Boot, but it is not officially supported.
And truth be told, Secure Boot isn’t all that secure either. It’s essentially just a failed attempt by Microsoft (under Steve Ballmer) to monopolize the hardware of the x86-64 and arm platforms and tie them to Microsoft Windows, because Microsoft was afraid of losing market share to GNU/Linux, and unlike Apple, they didn’t have a hardware platform of their own.
Secure Boot as a security precaution has already been exploited ─ albeit not in the wild yet. In my personal opinion, it’s junk, but Microsoft is on the UEFI committee, and so it was adopted into the specifications.
Important note: Disabling Secure Boot is not the same thing as choosing legacy BIOS support. My system here boots in native UEFI mode, but Secure Boot is disabled ─ it was a shop-built machine that came without an operating system installed, and I don’t do Microsoft Windows.