Installing manually
The generic setup instructions boil down to

1. Installing Python 3, including pip.
2. Creating a virtual environment somewhere: python -m venv OctoPrint
3. Installing OctoPrint into that virtual environment: OctoPrint/bin/pip install OctoPrint
4. OctoPrint may then be started through ./OctoPrint/bin/octoprint serve or with an absolute path /path/to/OctoPrint/bin/octoprint serve

This starts it up manually

/path/to/OctoPrint/bin/octoprint serve

https://community.octoprint.org/t/setting-up-octoprint-on-a-raspberry-pi-running-raspbian-or-raspberry-pi-os/2337

Basic Installation

cd ~
sudo apt update
sudo apt install python3-pip python3-dev python3-setuptools python3-venv git libyaml-dev build-essential
mkdir OctoPrint && cd OctoPrint
python3 -m venv venv
source venv/bin/activate

OctoPrint and it's Python dependencies can then be installed using pip:

pip install pip --upgrade
pip install octoprint