Build-time variable (ALLOWED_FRAME_URLS) was not added successfully

[huglemon]

I've been trying all day recently to add this ALLOWED_FRAME_URLS variable, but so far with no success.
As a beginner of Docker, I thought it was a normal environment variable at first, but after reading the documentation, it turned out not to be the case.
The last method I tried so far is as follows:

1. Create a Dockerfile with the following content:

FROM ghcr.io/umami-software/umami:postgresql-v2.13.2
ARG ALLOWED_FRAME_URLS=*
RUN echo "ALLOWED_FRAME_URLS: $ALLOWED_FRAME_URLS"

2. Because the default parameters have been given, execute the command directly: docker build --no-cache -t umami:inwind .
3. Redeploy

When building in step 2, ALLOWED_FRAME_URLS:* will be printed. I think this means it has been successful, but in fact it is not. frame-ancestors 'self' on my web page is still undefined
I want to ask, where might the problem lie now?
Do I have to add ARG ALLOWED_FRAME_URLS=* from the Dockerfile in the official git repository and build again?