OnePlus
Delete a Conversation in Messages auf OnePlus
The OnePlus Messages app treats each SMS or MMS thread as a single conversation. Deleting that conversation removes every message inside it in one step, so you don't have to select and delete texts one by one.
To remove a thread, open Open the Messages app ➔ Tap and hold a conversation ➔ Tap on Delete ➔ Confirm with Delete. The confirmation step exists because the action cannot be undone afterwards.
Any photos, videos, or voice messages that were shared inside that specific thread are deleted along with it. If you need those files, save them to your gallery or a cloud backup before confirming the deletion.
Deleting a conversation only removes it locally on your OnePlus phone. It does not block the sender, and it has no effect on messages stored on the other person's device or on any linked messaging service.
If you only want the thread out of sight temporarily rather than gone permanently, check whether your Messages app version offers an archive or pin option instead, since that keeps the content while hiding it from the main list.