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Ok, somehow the /var/www/html folder was set to read-only.  When I reapplied the correct permissions I was able to save my settings now.

You can close this.

Yes.  When I click the "Save" button, I see "Settings Saved" in the lower right.

Nevermind, I tried chaning APACHE_RUN_USER, APACHE_RUN_USER_ID, APACHE_RUN_GROUP, and APACHE_RUN_GROUP_ID and it worked.

Where do I configure them in the Docker container?  The Synology docker instructions don't say.