Yeah, all I could find was vague statements about the DNS server lookup order being “OS specific” and windows specifically being know for “not respecting DNS order”, see https://www.reddit.com/r/networking/comments/kb8hvt/dhcp_dns_server_order/

This is also supported by statements from pihole devs: https://www.reddit.com/r/pihole/comments/x2248t/is_it_worth_creating_a_second_pihole_dns_server/ And: https://discourse.pi-hole.net/t/primary-vs-secondary-dns/1536/4

And then there are the hundreds of similar questions which one could take as “evidence by quantity” or whatever.