I've this message vboxclient the parent session seems to be non-x11. exiting

[NuDub]

Hi
I installed VBoxGuestAdditions-6.1.8 and when I boot debian I have a black screen.
So I boot in recovery mode and type

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 startx

I have le message vboxclient the parent session seems to be non-x11. exiting
I found no solution on the net.
I download from windows an older version of guestaddition and I put it in my sharedfolder in automount.
I fund the shared folder in

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/media/

but when I type

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 ls

is return nothing as if no really mount
I don't know what to do

Thx for your help.