Nginx serving two Angular-Apps: Config with multiple location blocks causes issues - docker

Question

I created a website and a respective admin-backend with Angular and want to serve it using Nginx via Docker. The website should be available via 'mydomain.com/' whereas the backend should be available via 'mydomain.com/backend/'. Getting the website running works perfectly fine. But the path resolution for the backend just does not work.
This is my Dockerfile:
# Webpage
FROM node:16 as build-webpage
WORKDIR /usr/local/app
COPY ./webpage /usr/local/app/
RUN npm ci
RUN npm run build # ng build
# Backend
FROM node:16 as build-backend
WORKDIR /usr/local/app
COPY ./backend /usr/local/app/
RUN npm ci
RUN npm run build
# Nginx
FROM nginx:latest
COPY --from=build-webpage /usr/local/app/dist/webpage /usr/share/nginx/html/webpage
COPY --from=build-backend /usr/local/app/dist/backend /usr/share/nginx/html/backend
COPY nginx.conf /etc/nginx/nginx.conf
EXPOSE 80
The nginx.conf contains these location blocks:
location /backend/ {
root /usr/share/nginx/html/; # backend should get appended (due to root)
index index.html index.htm;
include /etc/nginx/mime.types;
}
location / {
root /usr/share/nginx/html/webpage/; # only / is appended, so webpage is appended manually
index index.html index.htm;
include /etc/nginx/mime.types;
}
When I then try to open 'mydomain.com/backend' or 'mydomain.com/backend/index.html', the following log is generated by Nginx:
open() /usr/share/nginx/html/webpage/backend/index.html failed …
As it seems to me, Nginx matches the "/-Location" instead of the "/backend/-Location", since the "webpage"-folder is part of the directory Nginx resolves.
According to various blogposts, Nginx chooses the "best-fitting" location branch when resolving a URL. Therefore, "/backend/" should be chosen. Also, I tried to replace location /backend/ with location ^~ \/backend\/, so that the caret enforces that branch since it is before the "/-Location" in the config file. Unfortunately, that made no difference either.
So I was blessed if someone could tell me what I'm doing wrong.
Thank you!