drag and drop not working only from host to guest

[science2002]

The Specs are listed below. To sum up them I had Win 10 as a host and as a guest with VB 6.1 latest.
I installed the guestAdditions, and I made biderectional both drag and drop and clipboard (they appear both in menus on the guest and in VB preferences).
Overall the clipboard works on both directions (overall, since sometimes I need to copy in the host more than once, to paste ok in the guest).
Drag and drop, works only from guest to host. But not from host to guest. In dragging a file from the host over a VB guest window (or desktop) the mouse's arrow turns into a sign of "red zone" (actually in black color).
I already tried to exclude UAC (User Account Control) on both host and guest. And I already tried to run explorer.exe with admin rights on both host and guest with no avail.
Logs are in attachment that are collected just after dragging a file from host to guest.
Where shall I look at to fix the problem: to the host or the guest machine? Are there some troubleshootings that can help to find the culprit?
Thanks in advance for any advice and support.

Host OS: Win10Pro 20H1
Guest OS: Win10 LTSC 2019 (latest)
Hw: Lenovo thinkpad P1 (intel i7), Oled Touchscreen
VirtualBox: VirtualBox-6.1.16-140961-Win installed as portable (with services working: I would like to keep it portable)