Only if the attacker has a valid certificate for the domain to complete the handshake with.
Relying on HTTPS and SVCB records will probably allow a downgrade for some attackers, but if browsers roll out something akin to the HSTS preload list, then downgrade attacks become pretty difficult.
DNSSEC can also protect against malicious SVCB/HTTPS records and the spec recommends DoT/DoH against local MitM attacks to prevent this.
> but if browsers roll out something akin to the HSTS preload list, then downgrade attacks become pretty difficult.
Can you explain why, considering it is at the client's side ("browsers")?
DNSSEC can't protect against an ECH downgrade. ECH attackers are all on-path, and selectively blocking lookups is damaging even if you can't forge them. DoH is the answer here, not record integrity.