I recently started using the "luci-app-https-dns-proxy" package on OpenWrt, which is preconfigured to use both Cloudflare and Google DNS, and since DoH was mostly unaffected, I didn't notice an outage. (Though if DoH had been affected, it presumably would have failed over to Google DNS anyway.)
Anecdotally, I figured out their DNS was broken before it hit their status page and switched my upstream DNS over to Google. Haven't gotten around to switching back yet.
And it’s not conspiracy theory - it was very suspicious when we did some testing on small, aware group. The traffic didn’t look like being handled anonymously at Google side
Although, perhaps, having an external VPS with a dns proxy could be a good middle ground?
https://developers.cloudflare.com/1.1.1.1/faq/#does-1111-sen...
I've also changed to 9.9.9.9 and 8.8.8.8 after using 1.1.1.1 for several years because connectivity here is not very good, and being connected to the wrong data center means RTT in excess of 300 ms. Makes the web very sluggish.
Quad9 has a very aggressive blocking policy (my site with user-uploaded content was banned without even reporting the malicious content; if you're a big brand name it seems to be fine to have user-uploaded content though) which this would be a possible workaround for, but it may not take an nxdomain response as a resolver failure
Clients cache DNS resolutions to avoid having to do that request each time they send a request. It's plausible that some clients held on to their cache for a significant period.