kitKAC's right that provider-side is where you actually want to solve this at that volume. The Tahoe cap exists because the blocked list is a synced JSON that ships to every signed-in device — Apple capped it when sync perf got ugly for people with 5k+ entries on iPhone/iPad.
If it's an iCloud address, build server-side rules from icloud.com > Mail > gear icon > Preferences > Rules. Those aren't subject to the cap and they run before anything ever hits Mail.app. For non-iCloud, the rules live at your provider — Fastmail's are fast and per-folder, Gmail's filters are effectively unlimited, Proton has sieve if you're on paid.