Your system is out-of-date. The current Plasma version in Manjaro Stable is 5.19.5, and kernel 5.6 is EOL.
In addition to the above, you’ve also missed the updates of a couple of essential components of the system for which manual intervention is needed. The first of that was GRUB ─ to patch it against the Boot Hole vulnerability ─ and the second one was an update to pambase.
Yes, sorry, I copied the text from my old post and forgot to change that. I’m currently on 5.7.19-2 and it still does not work. I’m going to try what @bogdancovaciu suggested above and get back to you guys.
That newer plasma is the KDE Plasma GIT version from unstable branch. To be honest is fine, but you must be quite patient with it and the fact that there are updates almost daily might not be what you like
Anyway, it resembles what Plasma 5.20 will be in a couple of weeks, few days after 2020-10-13