Ubuntu 22.04

First, build the Ubuntu 22.04 build environment docker image:
docker build -t chatterino-ubuntu-22.04-build -f Dockerfile_chatterino2-build-ubuntu-22.04 .

(alternatively pull from ghcr.io/chatterino/chatterino2-build-ubuntu-22.04:latest)

Clone the Chatterino repo with all submodules (will note it as /home/user/chatterino2 from now on), e.g. with git clone --recurse-submodules https://github.com/Chatterino/chatterino2

Build Chatterino in the docker image:

docker run \
    -v /home/user/chatterino2:/srv \
    -w /srv \
    --rm \
    chatterino-ubuntu-22.04-build '.CI/full-ubuntu-build.sh'

Now you'll have an executable you can use or package in /home/user/chatterino2/build

Ubuntu 24.04

See the 22.04 instructions above and replace 22.04 with 24.04