Only Flutter web relese build does not work - flutter

Question

When I run the Flutter web app in Android Studio using the run button or by flutter run -d Chrome, everything works just fine.
When I run flutter build web and open $(project_dir)/build/web/index.html, I get a white screen. There are these errors in the browser console:
Failed to load app from a service worker. Falling back to plain <script> tag. index.html:85:21
Loading failed for the <script> with source “file:///main.dart.js”. index.html:1:1
When I run flutter build web -v there is following:
[ +68 ms] Skipping target: web_entrypoint
[ +1 ms] Skipping target: gen_localizations
[ +311 ms] Skipping target: dart2js
[ +10 ms] invalidated build due to missing files:
/home/vanousek/prg/substance-mix/DOES_NOT_EXIST_RERUN_FOR_WILDCARD954977783
[ +72 ms] web_release_bundle: Starting due to {InvalidatedReasonKind.inputMissing: The following inputs were
missing: /home/vanousek/prg/substance-mix/DOES_NOT_EXIST_RERUN_FOR_WILDCARD954977783,
InvalidatedReasonKind.inputChanged: The following inputs have updated contents:
/home/vanousek/prg/substance-mix/build/web/main.dart.js,build/web/index.html}
[ +121 ms] Manifest contained wildcard assets. Inserting missing file into build graph to force rerun. for
more information see #56466.

Answer 1

When building your flutter app for web it's intended to be run on a web server.
Running flutter build web, would compile the project into a web project. You can use web hosting providers such as netify, firebase hosting, and Github pages.
Running the ./build/web/index.html would not show up. That's why you got the errors in the console.
You could run flutter run --release -d chrome to run on Chrome in release mode.
EDIT:
This is chrome DevTools, it seems that the site was looking for the main.dart.js and other resources.
I noticed it was pointing towards https://your_url/main.dart.js but the resource is located in https://your_url/substance_mix/main.dart.js. So it threw 404's.
One solution to this is to edit the index.html and add /substance-mix/ to all resources. Eg. change scriptTag.src = 'main.dart.js'; to scriptTag.src = 'substance_mix/main.dart.js';
or you can the GitHub Pages configurations. And have your website directly on https://mikulasvanousek.github.io/