First of all, uninstall the eos-hooks package, which keeps changing the data of /etc/os-release from a hook while installing base packages.

sudo pacman -R eos-hooks

Reinstall the base package group:

sudo pacman -Syyu --noconfirm archlinux-keyring bash bzip2 lsb-release coreutils file filesystem findutils gawk gcc-libs gettext glibc grep gzip iproute2 iputils licenses pacman pciutils procps-ng psmisc sed shadow systemd systemd-sysvcompat tar util-linux xz linux

Comment out the EndeavourOS repository and add the Arch community repo in the /etc/pacman.conf file.

sudo nano /etc/pacman.conf

#[endeavouros]
#SigLevel = PackageRequired
#Include = /etc/pacman.d/endeavouros-mirrorlist

[community]
Include = /etc/pacman.d/mirrorlist

Check for updates:

yay

All EndeavourOS apps will be listed as "not in any repos".

Use sudo pacman -R app-name to remove all of them. Handle the dependencies properly.

Reinstall other packages:

sudo pacman -Syyu --noconfirm breeze-grub breeze-gtk lsb-release

The default values of the name (aka. partlabel) and label of the root partition (if you did not set the name of partition during installation) are also "endeavouros". Of course, it means nothing.

If you don't like it, you can use parted which is CLI tool or gparted which is GUI tool to edit partition label or any other tools to change it.

Reboot and everything should be done.