Can I save and edit parts of a Netflix series (~ 20sec. As mp3) and use them in a hobby music project without commercial use?

Or is it then also a copyright infringement?

There's a nice page on the topic: The most common questions about music on Youtube

http://irights.info/artikel/die-hufigsten-fragen-zu-musik-bei-youtube/7244

Just read through and you will know afterwards.

As long as you have downloaded it legally and is only for your own (family / closest circle of friends) use, it is allowed and you have nothing to fear.

It looks different if you pass this on to others, publish it or give others access - then it is a copyright infringement.

Yes, if it's under 15 seconds long, you're even allowed to use it commercially.

Source?

The new General Data Protection Regulation Article 17: https://www.sueddeutsche.de/kultur/dsm-urherberrecht-world-wide-web-eu-richtlinie-corona-eu-urheberrechtsrichtlinie-1.5194814