Problems since theme and wp upgraded to latest versions

I suddenly no longer saw the + paragraph which I could change to, for example, insert an Envira Gallery. Instead there was a + in the top menu. If I clicked on this I could select a gallery - but it refused to appear where I had the cursor, going instead to the bottom of the page. I really don't know what sort of editor my theme uses, I suspect not the current promoted block editor.  I downloaded the plugin classic editor.  The interface is still quite different from before, but at least there is an Envira button I can click, and the gallery goes to the right place. However, I see that there is some deprecated code. ("<b>Deprecated</b>: Hook media_buttons_context is deprecated since version 3.5.0! Use media_buttons instead. in <b>/home/francesa/public_html/wp/wp-includes/functions.php</b> on line <b>6085")</b> I don't know about php and I don't think it appropriate to tinker with this file.  Can people confirm if a simple text edit should suffice? Also, is this theme being kept up to date?  I feel uneasy if there are problems after downloading latest versions of wp and theme.