There’s an increasingly infernal ‘makeover mania’ trend, which seeks to radically change perfectly good User Interfaces which people have spent years learning. Rescue your self-hosted WordPress install from that, at least, with the fine new Classic Editor plugin. Works with the latest version of WordPress, and is an official supported WordPress plugin.

You will not get the ‘center’ code on the old UI, which you do on the fancy one. This is replaced by a right-click addon such as ‘Paste email’ which you set to paste…

No need to add the end p tag. Here there are also Italics tags. I’m assuming you want a centred picture-title, in italics to clearly distinguish it from the body text.