Thanks a lot for your fast answer!
OK, now I understand, and I am going to take your advice and modify my system to UDP.
A few questions about it:
Is it a good solution when I use Wifi to connect the router with the tablet, because I have no ethernet port) or is there a better solution?
And is the RUT240 a good solution for it, or is this one also ok(https://www.amazon.de/GL-iNet-GL-SFT1200-Taschenformat-Gigabit-Anschlüsse-MicroSD-Steckplatz-White/dp/B09N72FMH5/ref=sr_1_27?__mk_de_DE=ÅMÅŽÕÑ&crid=179Y62K2UZTAP&keywords=wlan+router&qid=1655838805&sprefix=wlan+router%2Caps%2C123&sr=8-27) or is there a better one, or a reason why I should take another one?
Concluded it means that I have to connect the Arduino with an ETH Shield(https://at.rs-online.com/web/p/shields-fur-arduino/1763648) to the router.
The tablet would be connected via Wifi to the router.
Only with the F9P I am not sure. Have you meant with your last mail to keep the F9P via USB, or to connect it like here: F9P in ethernet mode ?
Thanks a lot for your help!