Immediately after switching the page, it will work with CSR.
Please reload your browser to see how it works.
Could you elaborate as you seem to be more "knowledgeable". This flag is clear at what it does and shouldn't be shipped into production. https://no-sandbox.io/
You can have a look where they specifically chose to force it https://github.com/signalapp/Signal-Desktop/commit/1ca0d8210...
There's an issue open to provide a flatpak for the app.