Just tried "EX file manager" and "FX file explorer" - both of which have been mentioned on the board here as previously working, but both errored out tonight.

So, Files by Marc it is: https://play.google.com/store/apps/details?id=com.marc.files

For simplicity's sake I'm just going to use honk.zip and honk.  honk is interchangeable with any plugin's zip and extracted zip

android/data/com.guildsoftware.vendetta/files/plugins - if there's not a plugins folder right there, the first thing to do before going dragging a plugin through the filesystem is create a plugins folder inside com.guildsoftware.vendetta/files

You'll need to use the default visible file manager/explorer or another app to extract the honk.zip into the downloads folder (where, most likely, your honk.zip landed).
The default visible(shown) file explorer will most likely not allow you to extract the contents directly into: android/data/com.guildsoftware.vendetta/files/plugins nor anywhere within android/data for that matter.

So get this tiny download from the play.google link above, it's a shortcut to open the hidden file explorer/manager that's part of android itself.

After you've extracted honk.zip , there's going to be a honk folder in the downloads folder (if you extracted to the downloads folder so the honk folder would land next to the honk.zip folder)

Open Files by Marc

navigate to downloads.

Here's the tricky part: you have to grab Honk (not honk.zip), keep ahold of it, and drag it through the file system to android/data/com.guildsoftware.vendetta/files/plugins by:

if using a mouse, just hold the left button down when the cursor is over Honk
if using touchscreen you have to hold finger on Honk until a checkmark appears, lift finger, then hold finger on Honk again.

While keeping ahold of Honk, hover over your device's name on the left then you'll see Android.
Still holding Honk, go hover over Android. When Android opens don't loiter over other things you want to go to data.
Again DO NOT hover over another folder.  The next one you're lookin for is com.guildsoftware.vendetta
Then files
then plugins
let go of Honk in an empty space, do not drop honk on another plugin's folder

don't know how long this discord link will work but here's a video of me doing it on a tablet that the left panel is just part of the screen all the time (really only matters for getting from downloads to "device", mine being named 'robert's tab s7") https://discord.com/channels/381426131334594573/381661985785511946/1355303430176116877
(this video is also below, annotated as tablet&mouse)

<s>There might be more coming from myself or a guildie about how to do this when that list on the left isn't just sitting on the screen</s>
s should be strikethrough but o well

EDIT: with assit from Ak'urabi who had to figure out how to do this without that list on the left already being there, see the attached vid that is annotated "if the list on the left isn't there all the time".  the dot is showing my finger touching the screen. If not using mouse you have to long press to get the checkmark then lift finger then put finger back down and keep it down to "grab and hold" the plugin folder (named DEMO in the vid because I'm demonstrating). Then you move it over to the very left of the Files app and there should be a blue bar that appears right before that left tray opens. When that left tray opens: hover over your device name, then go android, data, com.guildsoftware.vendetta, files, plugins and let go of it somewhere there's nothing else. You want to drop what you're carrying in the plugins folder, but not inside of another plugin. 

There's also a vid for if that list on the left is there (such as a tablet), and that one happens to use a bluetooth mouse.

Thank you xXxDSMer,

This is use full information, expertly explained.

I think you are the new Czar of phone installed plug ins!

o7,
GA