I.a. Upgrade/Install Erlang for Ubuntu version <= 18.04 LTS:
# For Migrating from old Bintray repo's versions
https://blog.rabbitmq.com/posts/2021/03/migrate-off-of-bintray/

# RabbitMq Team's PPA LaunchPad Erlang. Ref: https://launchpad.net/~rabbitmq/+archive/ubuntu/rabbitmq-erlang
sudo add-apt-repository ppa:rabbitmq/rabbitmq-erlang
sudo apt update
## Uninstall/Upgrade erlang. This will also remove depended installed RabbitMq old version 3.7/8.*
sudo apt-get purge erlang*

## Install erlang
sudo apt install erlang
# Or
sudo apt-get install -y erlang-base \
                        erlang-asn1 erlang-crypto erlang-eldap erlang-ftp erlang-inets \
                        erlang-mnesia erlang-os-mon erlang-parsetools erlang-public-key \
                        erlang-runtime-tools erlang-snmp erlang-ssl \
                        erlang-syntax-tools erlang-tftp erlang-tools erlang-xmerl

# Install Rabbitmq online repository and make it ready to install the rabbitmq-server package later
https://packagecloud.io/rabbitmq/rabbitmq-server/install#bash-deb

I.b For ubuntu version >= 18. Ref: https://www.rabbitmq.com/install-debian.html#installation-methods

II. Upgrade/Install RabbitMq to current version
## Add a new admin user
sudo rabbitmqctl add_user agm Ag@Rabbit2019
sudo rabbitmqctl set_user_tags agm administrator
sudo rabbitmqctl set_permissions -p / agm ".*" ".*" ".*"

sudo rabbitmq-server start -detached
sudo rabbitmqctl stop
# Web Management via port 15672
## Enable web management plugins
sudo rabbitmq-plugins enable rabbitmq_management

# Run Web management app
http://localhost:15672
user: agm
pwd: Ag@Rabbit2019

### Important notes on mis-match depencies errors. If it happened, we need to pin the erlang packages version to a right version not always the latest.
For example, for RabbitMq version 3.10.2, erlang must be < 25.* in Ubuntu 18 (bionic)
# /etc/apt/preferences.d/erlang
Package: erlang* esl-erlang
Pin: version 1:24.3*
Pin-Priority: 501