Paid users have option to enable/disable DNSSEC, though I’m not sure if it’s enabled or disabled by default. Bot specifically mentions that if you need/want DNSSEC support that you should subscribe to their paid service.
Their documentation even says “If you use Secure DNS protocols like DNS-over-HTTPS or DNS-over-TLS, DNSSEC provides virtually no value. Your DNS requests cannot be intercepted or spoofed by anyone.”
That’s actually not true because DoH/DoT protects you from snooping on your DNS queries, not from DNS spoofing or manipulation.