well lets just forget whatsapp for now and use conversations (google messages) because that is acting in exactly the same way, with same error but has no odd characters in its name.
❰greg❙~/.local/share/plasma_icons❱✔≻ cat conversations.desktop
#!/usr/bin/env xdg-open
[Desktop Entry]
Icon=/home/greg/.cache/favicons/messages_96dp.png
Name=messages.google.com
Type=Link
URL=https://messages.google.com/web/conversations?redirected=true
❰greg❙~/.local/share/plasma_icons❱✔≻That should work, as a last resort maybe put the web address inside quotes because of the ?redirected=true part at end…
No, but thx for trying 
Works fine if i execute it from terminal but if i click the panel icon it fails.
❰greg❙~/.local/share/plasma_icons❱✔≻ cat conversations.desktop
#!/usr/bin/env xdg-open
[Desktop Entry]
Icon=/home/greg/.cache/favicons/messages_96dp.png
Name=messages.google.com
Type=Link
URL='https://messages.google.com/web/conversations?redirected=true'
Well in that case, because the .desktop file is correct, it is a bug with plasma…
I was able to repeat the problem. It seems more wide-spread than OP describes.
It also affects other widgets, like Spectacle. It didn’t work at all. Nothing. I removed it and added it back and I got the “security” dialog, and the next time I got the error that the file is not valid.
The way I added it was to go to the menu, search for Spectacle, right click Spectacle and select “Add to Panel (Widget)”. Konsole, Kate, Dolphin all seem okay.
Maybe: Bug 428550 - Launching Desktop icons fails follow to 427797. Per Merge Request - FIXED-IN: 5.20.3
I had also created a “Link to Location” desktop file. Same issues. As mention in 427797 they will run from Dolphin.
Looks like he ahas a bigger trouble than mine.
Yeah, I should have stayed focused 
I was able to reproduce your problem. I do believe the Bug above addresses the issue.
Comment #10:
It only affects *.desktop files with a line “Type=Link”"
There are work arounds until 5.20.3…hhhmmmm
