Glinet support told me (a) "no, you cannot use usb WiFi on the Spitz; just buy this device XYZ instead" (which will use 14W not 3W, and is not even available yet), and (b) "yes, openWRT-22 is going to be released for the Spitz too, but maybe in 2-3 months". So I am stuck on openWRT-19.07.8 and without a USB device recommendation.
(3) antenna sockets
I bought the Spitz only a few weeks ago, and will not replace it with yet another device. And I don't want to buy-and-try many different USB sticks now, that's unecological. So I am wondering whether and how to solve my problem of shitty WiFi reception, by ignoring hotline (a) answer, with your help, and using simply any well documented USB pluggable WiFi adapter ...
From what I can see, what you have with their stock firmware is one that is OpenWrt-based, but modified. Whether you can access all the different USB dongles that OpenWrt supports depends on whether or not you can get access to all the OpenWrt packages, including kernel module packages.
The above resources (#1 above) talks about accessing the normal OpenWrt menus through gl.inet's menu. See if you can get into the LuCI System->Software page, which would let you install OpenWrt packages and kernel modules.
Also, whatever they have been telling you, there is definitely a version 22 firmware available for your device. And SNAPSHOT, if you want bleeding edge. From what I can see, putting it on will overwrite their custom UI that has OpenWrt as a part of it, with the standard OpenWrt and its UI. Whether or not you want to do that is up to you.
As it stands, though, until we can figure out if you have access to OpenWrt kernel modules, we can't tell you what dongles will work.
Wow, that "hardware page for my device" is truly incredible. Kudos.
Yes, I have installed packages via LuCI because out of the box, there was no "lsusb" command, so I used the software page of LuCI to install "usbutils". And that worked.
Please give me an example package name (that existed in 19.07.8) and I try that out right. Then we know, right?
For now (and unless that limits my choice of hardware dramatically), I would like to keep that 19.07.8 system that Glinet made, because (a) it's actually working, and I do like their added UI, and (b) in a few months they are going to officially publish their 22-version anyway.
This is what they call their fork, taken from LuCI:
Bottom of PCB, note location of connectors: Note that you can connect 3 additional pigtails for external wifi antennas, also if you want a mobile application with GPS, you could also hookup a GNSS/GPS antenna
I have never heard about "pigtails" before, but that seems to tell me that (without even going the USB dongle route) I could just buy those 3m WiFi antennas ... https://amzn.eu/d/0sB24H9 ...
... and then learn how to screw those 3m antenna cables onto the "pigtails"?
Wow, I wouldn't have thought it, but it looks like the external antennae are not WiFi at all but are actually for the 4G. All the WiFi antennae are internal. I would not have designed it that way. I would have put the WiFi external and the 4g internal.
Two wi-fi antennae are etched on the main board, one on a small daughter board on the back at right angles.
Those three connectors on the board are U.FL (a.k.a. I-PEX or IPX). What I would probably do is buy some rg178 cable U.FL to RP SMA Female (Reverse Polarity Female SMA connector) pigtails, drill 3 x .25" holes in the back of the case, mount the SMA connectors coming out the back, then connect three normal-ish wi-fi antennae on the back and see what that does for you. Something like this or this. Don't give any attention to the dB gain those ads claim - they are both about the same ~3dB, with the latter ones being very moderately (about 1dB) more efficient radiators.
Something like the way I have it configured on this homebrew device:
Of course, once you mount the connectors out the back, you can experiment with many antennae types and configurations.
WIth respect to the OS itself, I am not a fan of companies like gl.inet that make Frankenrouters with half OpenWrt married to their own weird stuff. You have no idea what they've done to OpenWrt, they are literally years behind the current, and what they've done severely limits the ability of communities like this to help. On two fronts. 1) It's harder for us to work around the junk they do to OpenWrt, and 2) not a lot of people here WANT to be a commercial company's support line to pick up the pieces of the wreckage they make of OpenWrt.
So whether or not you ever decide to use a new WiFi module in it, you might want to give some serious thought to getting pure OpenWrt on there. It's more up-to-date, more secure, there is far more expertise to help you with it, and the advice you will get will not be the advice of a commercial company who just wants you to buy more of their stuff. We don't here always agree on our advice, but it's always given with the best interest of the recipient.