I have found a VST host program that allows some major functionality with VST3 and OpenMPT.
This can be loaded as a VST in OpenMPT, allowing for use (bridge) of VST3!
Element VST2/3 Host : https://kushview.net/element/
Here is a download link for an older version, available without support :
https://github.com/kushview/Element/releases/download/0.41.1/element-win64-0.41.1.exe
I was able to use my Waves VST3 delays, reverbs, and compressors and others within OpenMPT and found no problems. VSTi instruments also worked!
Other brands of VST3 also worked
yes very handy kushview Elements!!!
as theres a shift taking place regarding VST's in that Steinberg are no longer giving out licenses for "new" development for vst2's so this bridging VST will become more useful as newer VST3's begin to flood the market
Steinberg are only renewing old existing licenses for VST2 updates from what i understand
Elements is not free, you must pay for a single download or pay monthly, I recommend some free alternatives such as VSTHost at https://www.hermannseib.com/english/vsthost.htm (https://www.hermannseib.com/english/vsthost.htm) for vst effects, I read that it can use vst3's as well and there is SaviHost at https://www.hermannseib.com/english/savihost.htm (https://www.hermannseib.com/english/savihost.htm) for vsti's, savihost can load vst3 instruments. There is also Carla at https://kx.studio/Applications:Carla (https://kx.studio/Applications:Carla)
Element is free software; you can compile it yourself for free. Obviously there are many free VST3 hosts out there; but neither SaviHost or VSTHost are VST plugins themselves that could be loaded into OpenMPT, which was the original topic here.
The link provided, for version 0.41.1.exe did not require the monthly or one time fee. The pricing model was added after that version.
Does Surge work with 0.41.1 version of Element?
I Used Surge 1.6.6, and it worked fine in Element. Version 1.6.6 of Surge, might be the last version that was VST2/VST3. If I remember correctly, newer versions of Surge are VST3 only.