You are right, I’m only fake support, just one that happens to have already setup RAK Pi based gateways and I originally diagnosed & solved this current problem for others here & on TTN forum.
I’m not sure I understand this - you’ve already done all the other things, but haven’t done the thing I’ve suggested twice. Or used the very very official authorised details on how to setup WiFi at the command line that I linked to.
For emphasis, others have had the problem you are having, it is unfortunate that the card image was released without a DNS entry, but they merely added the DNS entry and it then worked for them.
The first one is the one I followed when I setup my RAK7246 & then my RAK7248.
Both support pages have links directly to the latest firmware:
You can reach the support pages via the product page on the main website.
I appreciate you are frustrated. But you are not following the advice given to you.
As your SD card could now be in a bit of a mess, I’d go with re-burning it and starting over.