Display message with OMEMO content

When I send the first message to another user, the message “Blindly trusted OMEMO keys, meaning they could be someone else or someone could have” appears on the screen.
Please guide what it means?
Many thanks

This article describes what this means: Blind Trust Before Verification

I want to make sure that this message is not an error and that the messages I send through the Conversations app are all encrypted.
is it right.

The message is not an error, but a warning. This warning is a reasonable warning to get in certain circumstances (for example, when contacting a person for the first time).

With this explanation, there is no problem and can I trust the sending of messages and its encryption?

I cannot answer that for you. Please read up on the technology, and come to a conclusion that is applicable to your situation and environment.

Thank you for your reply