I believe that BASE_URL is a build time only variable and doesn't work at runtime.

It is possible to build your own Docker image with a custom BASE_URL. First you would have to git clone this repo then add the following to the Dockerfile:

# Add this before "RUN pnpm build"
ARG BASE_URL
ENV BASE_URL=${BASE_URL}

Then rebuild and run the container via:

docker build -t it-tools --build-arg BASE_URL="/my-folder/" .
docker run -d --name it-tools --restart unless-stopped -p 8080:80 it-tools

Then if you go to http://localhost:8080 you'll get a blank page, but opening the DevTools (& refreshing) you'll notice in the Network tab that the app is trying to fetch assets from /my-folder/...

So you would need to put another server in front of it, like Nginx Proxy Manager, Traefik, caddy etc. Then setup a reverse proxy pass using /my-folder