I am also experiencing this problem. I found this post from 2017 (Stop Reply All From Including Me), but it doesn’t include any useful information on how to fix it.
The problem is: someone sends an email to multiple recipients, including myself. When I “Reply All” to that email, I am included in the addresses my reply is sent to. This means that in my conversation view of the email thread, I see my message twice: once from my sent message, and once from the version of that message that I received (that I emailed to myself).
I would think that “Reply All” should not include my own email address by default or, at least, this should be an option for the user to choose the behavior. The current behavior does not seem correct.