Now it works. I needed to install peer dependencies on my own. So I added this to the end of the Dockerfile as well. The build works without errors.
This is what my dockerfile looks like now:
FROM n8nio/n8n
RUN apk --update add python
RUN apk --update add make
RUN apk --update add g++
RUN npm install -g n8n-nodes-suitecrm --unsafe
RUN npm install -g install-peerdeps
thank you so much for your help and input!