if you are on macOS, you can add a rule that moves or modifies some or all messages where senders have selected high-priority tags, such as sending the mail message into the trash if you are inclined.
Use rules to manage emails you receive in Mail on Mac - Apple Support
The available iCloud mail rules support is comparatively weak, and lacks this capability. Which means this filtering isn’t an option for iCloud mail on iPad or iPhone, unless you can also run a Mac (with rules) full-time.
Other mail-hosting providers can have differing filtering capabilities and features here.
IF you would like Apple to add rules selection criteria for iCloud mail, or on iPhone itself, send your feedback to them:
Product Feedback - Apple