It will prevent the ISP from snooping on, or tampering with, the DNS request. However when you go to use the IP you’ve retrieved via DoH/DoT; your first request establishing a TLS connection to that IP will contain an unencrypted SNI which states the domain you are trying to use. This can be snooped on by your ISP.
https://www.cloudflare.com/learning/dns/dns-over-tls/
If I understand it correctly DoH (which I use with NextDNS) should prevent ISP from snooping.
It will prevent the ISP from snooping on, or tampering with, the DNS request. However when you go to use the IP you’ve retrieved via DoH/DoT; your first request establishing a TLS connection to that IP will contain an unencrypted SNI which states the domain you are trying to use. This can be snooped on by your ISP.