before posting "it does not work" here and let us all scratch our heads why you don't try a bit harder yourself to get your problem solved.
Is the attitude really necessary? It isn't hard to be kind. World needs more of it.
The beginning of your response was helpful, though, so I thank you for that as it led to the resolution.
Anyway, it's been a long long time since I've had any issues with a MB. The last time I ever had to click on the Live Data tab, the only info there was the sensors. There are three sub-tabs now, which I didn't know about. I was looking in at the logging, which is really minimal now compared to how it used to be.
The issue was that the DNS lookups were failing. Which was weird, because a) only the WU destinations were failing and b) I could resolve the address just fine on my laptop, which is on the same network and uses the same address (that of the home router) for DNS resolutions as the MB.
Next step was to try an nslookup via the terminal app on my laptop. And, bingo!
% nslookup rtupdate.wunderground.com
;; Truncated, retrying in TCP mode.
So it appears if this happens on the MB, it
doesn't retry (maybe a future mod to add this?). But what changed?? It worked before!
I installed a new router last weekend. One of the new features I took advantage of is having the router use DNS-over-TLS for encrypted queries. Basically, every query that leaves the house (assuming the client is using the router's address for a resolver) gets encrypted and no one can gather data about where we're going on the internet. I pointed the router to Cloudflare's servers.
So, on the theory that the Cloudflare resolution was too big for the UDP query that the MB made, I set up the MB to manual assignment (the router is configured to give it the same IP address all the time anyway) which then allowed me to also bypass the router's DNS and point to OpenDNS instead.
And... everything is working again!