Well the first option is the one closest to what I have, it gives me similar results, I go between 18/21Mbps, sharing office I have my son, with the same hardware (I bought two computers exactly the same) with Linux Mint connected to the same wifi, and goes at 95/96Mbps. We both have dual boot with windows.
I probably shuffled something I shouldn’t have touched
Well, right now, I feel the same as I did in the first few seconds of the start of Slayer's Raining Blood 
I tried the two kernels that work for me, the linux-lts and the linux-zen (which I am using now), without seeing differences, the linux-next-git and the linux-mainline, they do not work for me, they do not let me start the system . As commented in other different posts by @tbg .
I have installed and reinstalled different iwlwifi and different drivers for RealTek from Pamac.
I have renamed the file /lib/firmware/iwlwifi-ty-a0-gf-a0.pnvm as it says in this post.
I checked that the dhcpcd.service and the networkmanager.service as described in this post did not work at the same time, and some other thing that I have seen on the Garuda and Arch Linux forums and that I do not remember now (I have broken the head), and the constant connection cuts of a second or two continue, they kill me, since I work from home managing one the content of a CMS and it gets stuck continuously. 
I'm about to reinstall the system again (I've already done it 5 times with the nVidia drivers issue), unfortunately, even though I like Garuda Linux, it's like fresh air, but if I don't get it either, I'll be sad to have to go back to some .deb branch, since, as I mentioned earlier, my son works fine with exactly the same hardware that I have.
Of course, I do not think it is due to a Garuda Linux malfunction, but because I do not know how to configure it correctly with the hardware I have. I'm just a hobbyist and some more technical tips I don't understand.
Maybe some step I have not done correctly, anyway if someone has an idea that I have not tried yet, apart from throwing me out of the window of course! 
Thnx!