It also seems to be not supported by PWAs. We use for example HaloPSA as a separate web app, and cannot use the extension anymore as the sidebar only opens in "normal" browser windows.

Agreed!!! the new sidebar is intrusive and has really turned the app into hot garbage any time I need to interact with it. We mostly use it for passwords and such and found the old interface way superior and clean/simple.

I understand it may be useful for some who need the extended features but a simple setting to revert to the modal interface is really needed