I highly doubt you’ll find any of the original Vst1 floating around..
I may have something on an the old Win machine..(Sony Laptop..350mhz 512kb RAM..10GB HDD..High End - for year 2000).
EDIT:
I found one from 1998..it is also .dll
1996 VST1 was an open source Sandbox released by Steinberg for Developiong VST..
1999 VST1 was replaced with..VST2 and it became the Industry Standard.
2008 VST3 was Introduced.
VST2 for Windows has always been a .dll file..(Dynamic Link Library) since it became the Industry Standard…
VST2 for mac has always been .vst (supposedly cross platform with Windows)
VST3 has always been .vst3.
Win = dll(Vst2) or .vst3
macOS (Intel) = .vst (Vst2) or .vst3
.vst (Vst2) is Not compatible (Rosetta) with Apple Silicon macs and Steinberg never developed a VST 2 SDK written in ARM64 for Apple silicon
As far as Future Development of VST…
I am a member of the The MIDI Association.
In 2020 MIDI 2.0 was adopted and as of last year 6 MIDI-CI (Compatibility Inquiry) Profiles were Voted/Adopted.
The past year has been focused on Drums which there will now be (2 )Drum Profiles…so there are a total of (8) New MIDI Profiles.
MIDI-CI DEFAULT DRUM NOTE MAP
Which is based on what everyone is currently using since the 1980’s.
Note there is now a Recommended Pan Position for each Instrument.
and
MIDI-CI DRUM PERFORMANCE PROFILE
This is designed specifically for Electronic Drum Kits and will allow direct communication with Drum Software.
It is past due as it was to be voted on/adopted in July 2025..
I suspect after it is Adopted and should be the last of the MIDI-CI Profiles you may see Steinberg release a VST4 SDK within the next couple years or possibly sooner.
There isn’t any literature or Documents..I only have 1 Video..
MIDI 2.0 DRUM PROFILES
If you want to follow what is going on with VST3..here is the Developer Portal