If anybody is facing the same problem: after installing StellarMate on a Mele Quieter 3Q, I found out, that WiFi speed of the device was only 802.11g (54mbit/s). The WiFi hardware of the mele supports 802.11ax and my router supports 802.11ac. The WiFi hardware of a mele is from Intel and in Ubuntu this is managed by the kernel module „iwlwifi“. The settings of this module is stored in /etc/modprobe.d/iwlwifi.conf (The setting options can be obtained with „modinfo iwlwifi“). In the conf file I found the setting „options iwlwifi 11n_disable 1“ which limits the WiFi speed to 802.11g. I just deleted this line and after a reboot StellarMate/Mele connected with 802.11ac. The system is now very snappy. Image downloads take now about 1.5sec, before it was round about 40sec. Looping for a first manual focussing or polar alignment are now very convenient (I run KStars/Ekos on a laptop and connect to StellarMate on the Mele).

Thank you so much for this.
I noticed the speed jump straight away.

I found it a bit odd why the RPi4 with an external dongle using Wifi5 was a lot faster then the Mele 3Q, as the RPi4 was transferring images up to 5secs and the Mele was taken 20secs for a transfer.

Instead of deleting it, change the 1 to an 8.
Generally 8 is the most helpful option to use as it is to enable agg TX.

What about if you added a # in the beginning of the line, would that not have ignored the line?

Commenting it out would do the same as deleting it, and you have the ability to un-comment it if needed to change later.
I always recommend commenting something out instead of outright deleting it in case you need to go back later. I also place a comment line above what I comment out describing why I did it since I won't remember later most likely.