This is a script to convert a Manjaro installation to an Arch installation with a single command.
The original version is this gist which did work but wasn't seamless.
This script follows the GPLv2 license in the original script.

• Support for all editions except Sway Daily
• Nvidia drivers reinstall
• Change UEFI boot entries
• Change mirrors
• Change kernel with Arch's
• Change Manjaro stuff in /etc
• Purge Manjaro stuff
• Change theme to default in KDE Plasma

A few months ago, I was using Manjaro just because I liked the green theme, and I just wanted to compile paru.
The libalpm library and pacman, which recently had a major update at the time, weren't updated in Manjaro's mirrors, but paru already had an implementation of the updated versions.
I did manage to compile it by switching to an old tag, but it was very inconvenient, and I decided to switch to Arch while preserving my userspace. Online guides of it were wrong in many ways, and I finally found a working script which did work, but was incomplete. I decided to improve it, and the result is this.

The main difference of pure Arch and Manjaro is that they use different mirrors. Manjaro uses slightly old versions of a package for testing, so changing it to Arch mirrors is the first step.
Then the script deletes Manjaro-specific packages and Pacman configurations, and enables the multilib repository if it's commented out.
After that, the script performs a pacman -Syyuu so that the packages are updated and installs an Arch kernel.
Finally GRUB is updated to have Arch's theme and the distributor name is changed to Arch by installing lsb-release from the Arch Linux website.
Finally DE-specific operations are performed to give a better polished result.

The screen goes gray after rebooting after running this script.
As far as I have experimented it's definetely not a Wayland issue, it's an issue in Sway, probably because Manjaro configs are all deleted. Please DO NOT USE THIS IF YOU'RE ON SWAY!

• Check if UEFI or legacy BIOS

• Choose a different editor other than ${EDITOR}

• Ask reboot after run

• Ask which kernel version is to be installed

• Manjaro Sway community edition support