How to convert non-portrait photos to support background blur on iPhone 12 Pro?

Hello,

Background blur is only available for portraits. Unfortunately several times i take photos which i later would like to have background blur, but i cant do it for photos and i cant convert the photo to a portrait.

I read that conversion from photo to portrait is only possible in new iphones. I have an iphone 12 pro and i suggest a simplified feature to convert could be easier (generic not only humans, dogs and cats) and that all fairly current models would support this simplified service.

Thanks for considering my question.

[Re-Titled by Moderator]