For Cards View, see this topic: https://support.mozilla.org/en-US/questions/1462837#answer-1673571

For Table View, the text has the tag colour by default, but to colour the background, use this add-on:

https://addons.thunderbird.net/en-us/thunderbird/addon/tag-toolbar/

Thanks, it worked - but the colors had so high opacity that I couldn't even read was in the box when it was tagged with the blue color. Is there a way to reduce this? (and without reducing the opacity of the text also)

Post a screenshot to show what you mean. Note that the tag colours can be edited in Settings.

Thank! Everything is how I like it now 😊

As said, everything worked - but now suddenly, the text is not visible if a message is tagged (this has been the case for the last couple of days). Edit: The text becomes visible though when I click on the specific message

Post your css for the tagged message. It's possible to use something like [selected="false"] to set the text colour of deselected messages.