Have you used 1:1:1:1 service by Cloudflare

Yes, but many hotel wifi networks didn't like me setting my own DNS servers so I have to switch it off regularly. I uses it as secondary on servers in case the hoster's DNS is down (well, ok, it only happened once).

I noticed that some of the cloud hosting services are slow when I connect to 1.1.1.1. For example I have some sites on Digital Ocean and the latency is super slow. I had to disable it because of that

Yes, but they recently had a major outage that caused a lot of issues for me. I have since reverted back to the Comcast defaults of 75.75.75.75

Before Firefox implemented dns over https, yes, after that I felt no need to tinker with the dns anymore.

Yes, but I vastly prefer NextDNS.

Yes