I suggest taking a look at your html sanitization settings make sure html isn't allowed in markdown settings.
Next step would be to move the other 2 topics from that category and check if you still see broken markup.
I'm wondering how i can change the user profile display?
As i see in ACP > widgets, there are 2 templates, global and groups/global.tpl. I guess i can add something like users/global.tpl to change widget management on their pages but i don't know how.
Also, i have found the custom field plugin but for some reason, custom fields doesnt not appear on profile page. As i see on it's readme.md, i should import a template, so maybe it's related
NodeBB 1.x.x, Persona, Flex Version (insert link on template in user's profile template wherever you like): <!-- IMPORT partials/account/custom_fields_flex.tpl -->
So i guess it's the same thing but i just don't know how to do it.
You need to modify the .tpl files in your theme.
To use that plugin you need to add that line whereever you want to in the theme template below and restart.
You need to define the widget area in the template, and let nbb know they exist using the getWidgetAreas hook.