So here is how you can use Reaper Plugins in LMMS with YSFX open-source vst3 plugin loaded in Element By Kusview :

Download Element by Kushview from github, version : 0.41.1
Download YSFX VST3 Plugin from github, the latest version

Download any or all of these recommended repositories of Reaper Plugins from github:

TukanStudio Plugins - top recommendation
JSFX by JoepVanlier - top recommendation (beatmakers who use LMMS to make beats will have a beautiful surprise with one of the plugins, but they are all top)
Sonic Anomaly JSFX Plugins Implementation from originals - top recommendation
Geraint's JSFX
JSFX by chkhld

Tip : You can always find other plugins or packs of plugins by searching "jsfx plugins github" on google or "jsfx plugins" on github search directly.

Now a quick tutorial for how to open them :

Install Element by Kushview, do not forget to install the vst2 version in your vst folder that you use with LMMS
Extract YSFX folder in Program Files/Common Files/VST3 Folder
Extract the folder, as example TukanStudio Plugins in your ysfx folder
Open LMMS, open Element by Kushivew with VesTige or from mixer channel, which you will use often, because many of them are effect plugins, after that go to your ysfx folder, drag the ysfx.vst3 plugin into Element and do not forget to connect the modules in Element for audio input and output.There is midi input to midi output (the orange dots) and audio input to audio output (the green dots), which will be 2 to 2, otherwise you will hear the sound in just one channel. Now you have opened the ysfx plugin, go to load button and open a jsfx plugin from the tukanstudio plugins, for example Lexikan.
Be patient, sometimes the graphics will load a bit slower.

Enjoy Reaper Plugins in LMMS and have fun making music!