You can find the right filter here: https://www.galaxus.ch/de/s2/product/patona-hepa-filter-levoit-core-300-1-x-zubehoer-luftbehandlung-35819346.

I currently have 900 operating hours on the Core 300S, which indicates that the filter still has 80% of its service life. So there is an indication of when the filter should be changed. However, I think that this information is calculated from the operating hours and the device cannot really measure whether the filter is "used up / full".

Yes but it’s covered in plastic wrap make sure to take it off before starting the machine. They also offer 3 different versions of filters depending on environment .

240 m³/h is correct. Thank you for your comment. I have passed this on to the relevant department for correction and it will be dealt with as soon as possible.

That's right! Usability is not restricted without the app.

The simplest, i.e. the Euro plug (plug type C: CEE 7/16). https://de.wikipedia.org/wiki/Eurostecker#/media/Datei:Euro-Flachstecker_2.jpg