Don't think too much, you have an old WiFi adapter and not suitable for multimedia, not even using Windows. Your adapter could theoretically work but the requirements are so demanding that this is highly unlikely (the biggest problem in the 2.4GHz band is interference). Buy an adapter that works on the 5GHz band and your problems will disappear if your access point is not far away and the level of interference is small. Despite everything, from time to time you will see frozen images for a few moments.
Also take the opportunity to look at wikipedia something about WiFi networks Wi-Fi - Wikipedia, taking into account that the theoretical maximum speeds are half the link speed because they are half duplex links.
I understand your point but don't take me the wrong way, maybe my English is a bit bad and I don't express myself correctly.
I live in Argentina, for several years this country has problems with the importation of products and if there is a very specific 5ghz model, the truth is that it is very unlikely that it exists in the local market, importing the product is a possibility (difficult, but possible) but the reality is that there is not a detailed list here (and from what I investigated in this forum there will not be) of dongles or wifi antennas that work directly out of the box, in fact yesterday I bought the Tl-WN722n because I read in this same forum that it worked (and it's true, it works but halfway)
As I told you, this does not have to do with interference and 2.4ghz bands since in my router I have an option to "scan" the other nearby wi-fi and see what channel they are on, yesterday I put my wifi on a channel that does not It was in use by nobody (neighbors), with the same usb extender I put the antenna literally 1 meter (3.3' feet) from my modem / router and the speed it received was the same (maximum 20mb) the antenna picks up and supports up to 150mb and my internet ranged between 300 and 320mb so if I would be receiving half of that I would be more than satisfied, I would be more than satisfied honestly, even with only 50mb.
Nor is it the wifi antenna since testing on a windows pc the mbps it receives is much higher (from 30 to 50mb)
As you can see this problem has already been solved in Ubuntu, but since LibreELEC is a custom linux for what I understand is not possible for the user to install those things.
wireless - WiFi connection run very slow in Ubuntu 16.04 (USB Stick) - Ask Ubuntu
wireless - Internet speed slow on Ubuntu 18.04.1 with TP-LINK TL-WN821N - Ask Ubuntu
networking - Internet speed really slow in linux but not in Windows - Ask Ubuntu
My ethernet speedtest :