

Haven’t used Kubuntu so can’t help you with that.
Regarding installing application from 3rd parties, there is no guaranteed way to know that what you’re installing is clean.
That being said, I would argue basic evaluations (how long has the project been around, does it get mentioned a lot in articles and forums, are there a lot of star and activity on the guthub page?) should be good enough for regular operational security.
One other general tip, try using Gemini (the LLM by Google) for real-time support and explanations around Kubuntu. I find it helpful for guidance on complex applications (ones that are far more niche than Kubuntu).
This is not an internet issue, this is a socio-political issue.
We have yet to figure out new modes of governance, economic relations and political systems that take in account the reality of a society with universal, high quality ICT access.
The fact that it is far easier to spread misinformation is a social issue, not a technological issue. It’s driven by the fact that US technology oligarch only care about engagement and they hold no responsibility for their actions (and cannot be prosecuted due to broad support for corruption and criminality in American society).