Move the REPO and WEBROOT vars to the Dockerfile since that's the only place they're needed. Dir is getting created successfully now.

Config/F-DroidRepo/Dockerfile

@@ -8,9 +8,9 @@ FROM debian:trixie-slim
 # Setup #
 
 ARG REPO
-ENV REPO="$REPO"
+ENV REPO="/root/fdroid"
 ARG WEBROOT
-ENV WEBROOT="$WEBROOT"
+ENV WEBROOT="/var/www/html"
 
 USER root
 RUN mkdir -pv "$REPO"
@@ -19,9 +19,9 @@ WORKDIR "$REPO"
 # Install Packages#
 # https://f-droid.org/en/docs/Installing_the_Server_and_Repo_Tools/#debianubuntumintetc
 
-RUN apt-get update && apt-get install sudo bash curl git vim nginx
+RUN apt-get update && apt-get install -y sudo bash curl git vim nginx
 COPY files/debian-backports.sources /etc/apt/sources.list.d/
-RUN apt-get update && apt-get install -t trixie-backports fdroidserver
+RUN apt-get update && apt-get install -y -t trixie-backports fdroidserver
 
 # Generate F-Droid Repo #