<p>In all the bigger prints I print on my Ender 5 with PETG I have problems with warping and raft detachment during printing. I have a glass bed and I'm using Ultimaker Cura 4.6.1 standard printing settings for PETG (Recently I had some success using 245 °C nozzle temperature and 80 °C build plate).</p>
<p>Any ideas how to reduce those problems?</p>

This sounds like a bed leveling issue.  As reported by others, I get much less warping with PETG than with ABS or even PLA, and deal with too much adhesion with PETG rather than too little.  With a Reprap x400, I printed a faceplate for the extruder to hold a electronic drop indicator.  This gives me much higher precision leveling. Of course, I remove the drop indicator after leveling.
If leveling isn't the issue, then you may be printing too fast.  The recommendations I've seen are to print PETG at 50 mm/s or less.  I print a a lower speed than that.