Akregator and KMail uses probably HTML to display some content (not news channel or e-mail content, but UI elements). Problem is, UI elements written in HTML doesn’t display on my system. There’s only a text. Link to image: https://i.imgur.com/GXHZt9w.png . Problem appear before upgrade to Plasma 5.19 .
Sorry, but I do not see what you mean. While I can not read the Polish in the image, to me it looks like a correct formatted text.
BTW, you could use https://susepaste.org/ for your images. Not everybody likes commercial sites with all sorts of scripting and cookies.
Bug has already been reported, fix upstream is done and will be in one of the next TW snapshots.
It is fine you see what the problem is, but I don’t 
Any hints to increase my eyesight?
The mail preview heading is broken, emoji are not rendered. Seeing this myself I was going to report a bug, but it was already there.
It’s not your eyesight, Henk. If I hadn’t seen it myself and reports on the Discord server and the Telegram groups, I wouldn’t have understood either.
Thanks for the answer and trying to help me to understand it.
To be fair, I reread every piece of text in that image of the OP, but see no strange things. Let alone “HTML build-in content” (btw I admit that I do not realy understand that also, most often when people say something like that, it means that you see the HTML tags and thus not their results, but I do not see a single < or > in the picture)
Also I see no uninterpreted emojis. I see no imojis at all, nor as picture, nor as character combinations. Also, I am not sure what emojis have to do with HTML. E.g. the emoji in my post a bit back, being :(, is to be found in the HTML-page of this thread as
<img src="images/smiliesnew/sad.png" border="0" alt="" title="Sad" class="inlineimg" />
Just an image, no HTML by itself.
But, let it go. The OP has an answer and let us hope it is repaired soon.
Before update, akregator’s main screen display a nice background and images at heading. This is not frustrating bug, but always a bug. Sorry for bad English,