MariaDB Server failure on Proxmox (with Ubuntu 20.04 and Systemd)

Hello,

Just after installing MariaDB server & client, I am getting the following errors:

Setting up libdbd-mariadb-perl (1.11-3ubuntu2) ...
Setting up mariadb-client-core-10.5 (1:10.5.4+maria~focal) ...
Setting up mariadb-client-10.5 (1:10.5.4+maria~focal) ...
Setting up mariadb-client (1:10.5.4+maria~focal) ...
Setting up mariadb-server-10.5 (1:10.5.4+maria~focal) ...
locale: Cannot set LC_CTYPE to default locale: No such file or directory
locale: Cannot set LC_MESSAGES to default locale: No such file or directory
locale: Cannot set LC_ALL to default locale: No such file or directory
Created symlink /etc/systemd/system/multi-user.target.wants/mariadb.service → /lib/systemd/system/mariadb.service.
Job for mariadb.service failed because of unavailable resources or another system error.
See "systemctl status mariadb.service" and "journalctl -xe" for details.
Setting up mariadb-server (1:10.5.4+maria~focal) ...
Processing triggers for systemd (245.4-4ubuntu3.1) ...
Processing triggers for man-db (2.9.1-1) ...
Processing triggers for libc-bin (2.31-0ubuntu9) ...

systemctl status mariadb.service
Failed to dump process list for 'mariadb.service', ignoring: Input/output error
● mariadb.service - MariaDB 10.5.4 database server
Loaded: loaded (/lib/systemd/system/mariadb.service; enabled; vendor preset: enabled)
Drop-In: /etc/systemd/system/mariadb.service.d
└─migrated-from-my.cnf-settings.conf
Active: failed (Result: resources)
Docs: man:mariadbd(8)
https://mariadb.com/kb/en/library/systemd/
CGroup: /system.slice/mariadb.service

Jun 30 06:43:57 web3 systemd[1]: mariadb.service: Will not start SendSIGKILL=no service of type KillMode=control-group or mixed while processes exist
Jun 30 06:43:57 web3 systemd[1]: mariadb.service: Failed to run 'start-pre' task: Device or resource busy
Jun 30 06:43:57 web3 systemd[1]: mariadb.service: Failed with result 'resources'.
Jun 30 06:43:57 web3 systemd[1]: Failed to start MariaDB 10.5.4 database server.

Service does not want to start. The issue seems related to Systemd.
I am able to run mariadb server manually using

cd '/usr' ; /usr/bin/mysqld_safe --datadir='/var/lib/mysql'

I tried with a brand new container on my proxmox server:

pct create 131 local:vztmpl/ubuntu-20.04-standard_20.04-1_amd64.tar.gz -hostname "web3.domain.com" -arch amd64 -cores 2 -memory 512 -swap 512 -net0 bridge=vmbr1,name=eth0,ip=10.0.1.1/24,gw=10.0.1.254 -onboot 1 -ostype ubuntu -rootfs local:30

pct start 131

pct enter 131

apt-get update

apt-get full-upgrade

apt-get -y install traceroute aptitude byobu software-properties-common nano curl

curl -LsS https://downloads.mariadb.com/MariaDB/mariadb_repo_setup | bash

apt-get -y install mariadb-server mariadb-client

AskUbuntu: https://askubuntu.com/questions/1254782/unable-to-install-working-mariadb