While reading the handbook chapter on the Mixer, one might get the impression that all of this works on every supported OS.
But it does not (and probably never will)
I have a 4.1 beta for Linux compiled with VST re-enabled.
=> deleted. see below
Most Linux VST's do not show a gui, but some do work: e.g. 3Vstudio Orchestools and Decentsampler (amongst others)
Also work: (almost all) Windows VST3 with yabridge (provided they can be made working with wine in the first place), e.g. Spitfire BBC discover/core, Spitfire Labs, Miroslav Philharmonic 2, Sampletank, Kontakt, ...
The Linux version of Kushview elements rack-plugin vst3 also works. This one can load Linux VST2, VST3 and LV2 plugins. It's working reasonably well (for the most part).