Just a perspective - 300k DNS queries is not very much. 1 full day of home use + work (most DNS goes over VPN for that) and I am at 130k queries. So you'll get a nice little trial, but don't expect it to last very long, imo
I've been using NextDNS now for half a year or so and I have 1,021,075 queries in the last 90 days, or roughly ~11k a day. I have ~69k in the past 7 days.
I have this set up on all my devices.
Are you running a home server or something that could explain so many requests?
Haven't managed to track it down.
2 Windows 10 machines make a LOT of phone-home queries.
Nextdns has a cache boost option now which sets TTLs to a minimum of 5mins. If the client is complaint (respects the TTLs), then that should help further.