Okay... I just went to the ArchLinux wiki article on Visual Studio Code and played with the ELECTRON_TRASH variable. Supposedly the default is gio but I think under KDE it is set to kioclient5 or kioclient.
So, the solution is to launch Visual Studio Code like this ELECTRON_TRASH=gio code, after that file/directory moves to the trash bin are instant.
To fix this for now, I have created the file ~/.config/plasma-workspace/env/electron-trash-gio.sh with the following content
Thanks for creating this issue! We figured it's covering the same as another one we already have. Thus, we closed this one as a duplicate. You can search for existing issues here. See also our issue reporting guidelines.