Slower DNS

diag output: https://nextdns.io/diag/05cf7b80-fd87-11ee-8172-c32f8a4c21b1

The route with IPv6 DNS has always been outside Brazil (anexia-mia). With IPv4 the tendency is to select a nearby location, but rarely the best latency, giving preference to edgeuno-poa, but the best is "edgeuno-cwb".
At times I observe great oscillation, changing between edgeuno-cwb, *-sao, edgeuno-poa and anexia-mia.
How does NextDNS determine lowest latency?
This is using Windows 11.
I'm monitoring the behavior with DoT on Android, and the selection has been good, always choosing the lowest latency (edgeuno-cwb), but I see that it prioritizes always using IPv4, despite my network and device using IPv6.