Here is installation instructions, how I succesfully install MeschChat on Raspberry Pi 4B and Raspberry Pi Zero 2W.

OS: Raspberry Pi OS Lite 64-bit (Bookworm 12.11)

Source links

https://www.youtube.com/watch?v=Hzq_imh79DM video.

https://github.com/liamcottle/reticulum-meshchat/blob/master/docs/meshchat_on_raspberry_pi.md instructions.

Prerequisites

$ sudo apt update
$ sudo apt upgrade

$ sudo apt install git
$ sudo apt install python3-pip

NodeJS v22 install

$ curl -fsSL https://deb.nodesource.com/gpgkey/nodesource-repo.gpg.key | sudo gpg --dearmor -o /usr/share/keyrings/nodesource.gpg
$ NODE_MAJOR=22
$ echo "deb [signed-by=/usr/share/keyrings/nodesource.gpg] https://deb.nodesource.com/node_$NODE_MAJOR.x nodistro main" | sudo tee /etc/apt/sources.list.d/nodesource.list
$ sudo apt update
$ sudo apt install nodejs

MeshChat install

export NODE_OPTIONS=--max-old-space-size=512 This is important on Raspberry Pi Zero 2W. Without this I cannot build web frontend with npm run build-frontend (memory exhausted). 
$ echo 'export NODE_OPTIONS=--max-old-space-size=512' >>~/.bashrc
$ source ~/.bashrc
$ git clone https://github.com/liamcottle/reticulum-meshchat
$ cd reticulum-meshchat
$ pip install -r requirements.txt --break-system-packages
$ npm install --omit=dev
$ npm run build-frontend

Setting MeshChat as systemd service

$ sudo nano /etc/systemd/system/reticulum-meshchat.service
[Unit]
Description=reticulum-meshchat
After=network.target
StartLimitIntervalSec=0

[Service]
Type=simple
Restart=always
RestartSec=1
User=jirka
Group=jirka
WorkingDirectory=/home/jirka/reticulum-meshchat
ExecStart=/usr/bin/env python /home/jirka/reticulum-meshchat/meshchat.py --headless --host 0.0.0.0

[Install]
WantedBy=multi-user.target
Starting service
$ sudo systemctl enable reticulum-meshchat.service
$ sudo systemctl start reticulum-meshchat.service
$ sudo systemctl status reticulum-meshchat.service

It works!