I think it’s not possible (but feel free to prove me wrong ;)) so here comes an idea:
I like to see mails in HTML, but for security reasons, the Junk E-Mails should be stay on plain text views, so HTML could not be interpreted.
For this an option would be great to decide, if Junk E-Mails stays on HTML as the rest or would displayed as plain text.
Unfortunately eM Client does not currently offer displaying of message format based on which folder you are viewing, so you are not wrong on that.
But by default messages will not download the linked content specified by the HTML, so no links will be followed. In this case it really does not matter if this is displayed as plain text or not. If the content is embedded in the message, then that will be displayed, so if it is offensive, try not to look at it for too long.
But there should not be any security concerns with the default setting which you can check in Menu > Tools > Settings > Mail > Privacy. The default option will only download content for named senders. This applies to all messages, so even those spam messages that make it to your Inbox will be displayed according to the settings.