No install dual boot

[Wollie]

Welcome here, @wyatt

Have you follwoed this guide?

[root tip] [How To] Dual boot Manjaro and Windows

Difficulty: ★★☆☆☆ Dual boot - Step by Step Target systems Firmware Checklist Windows preparation Manjaro installation Revisions Target systems UEFI Computers with preinstalled Windows (Windows 10) is computers using UEFI firmware. This guide is a generic guide targeted at UEFI installations. However some of the guide does apply even if you are using a BIOS/MBR setup. If you are using a BIOS/MBR (DOS) partition schema watch out for this Skip if using BIOS/MBR To ensure a …

See if this Arch wiki entry provides some help for you:

Troubleshooting - Dual boot with Windows - ArchWiki