Is any MCU board supported by LabVIEW 2020 yet? Is add-on required or not?
No! NI has more or less given up on trying to support arbitrary third party embedded controller boards through the Embedded Toolkit (AD Blackfin and Windows CE was long ago discontinued and the ARM Toolkit hasn't received any updates for recent LabVIEW versions). And yes this Toolkit is an extra paid option to LabVIEW.
Instead they support besides their own ARM based realtime targets a few selected boards for non-realtime use through the Linx Toolkit, namely the Raspberry Pi 2 Model B or newer and the Beaglebone Black board. This is a much more direct experience as you can basically deploy your LabVIEW VIs directly to the controller board without having to go through exporting it into C++ source code and getting your embedded cross compile toolchain to play nicely with these sources. It does have the limitation that it only works on the boards NI explicitly created a target system for.
But while you could theoretically use the ARM Toolkit to create executable code for most ARM based targets, the reality was that almost nobody got it to work for other targets than what NI provided examples for, since setting up your cross compile toolchain correctly to make it compile the LabVIEW created C++ files was a major challenge that only very experienced embedded developers could manage and they are the last ones who will bother with LabVIEW to create an application for their board.
The nice thing is that the Linx Toolkit is free to download. It is also part of the LabVIEW Community Edition, which you can use for free, but only for non-professional projects. Basically if you make any money with the project you create, even if it is in the form of fees to teach someone else, you are not allowed to use the Community Edition. But if you have a fully licensed LabVIEW version, you can install the Linx Toolkit into that version and create applications to run on those boards that you can sell.