Having eventually fixed the issue, I answer to myself, to share my experience with everybody.
Actually, my accesses to remote computer are un-authentified accesses (mainly because I do not have the same user accounts defined on the different computers of my LAN)
And indeed, opening a session on remote computer was very long, even outside of QAP, at least first time. Once established, subsequent accesses were fast (except in QAP...).
And in more, if on one side I was able to access remote shares providing their full UNC
\\ComputerName\ShareName
on the other hand I was not able to get the list of available shares.
This was a second drawback, and I searched how to fix it.
Actually, it was, because the registry value "restrictanonymous" in "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa" was set to 1
Since I set this value to 0, I'm able to get list of shares of remote computers (remote but close, since on my home LAN) which was my 1st goal.
But also, even first access to remote computers is very fast... and all accesses via QAP are very fast as well.
FYI, I found this parameter "restrictanonymous" here :
http://networking.nitecruzr.net/2005/07/...erver.html
This website is quite old, and maybe no more 100% accurate, but on the other hand, it's the first time I found a site explaining in an understandable way local networking, and how troubleshoot it !
As far as I have understood (after searching on Internet after fixing my issue, but I'm not sure), when anonymous access is "restricted", Windows tries several method to nevertheless establish session, and this takes a lot of time. Once session is set up, access to data themselves is fast.
I guess that each access via QAP established a new session (and then each access is "first" accesss), that could explain strange behaviour I got.
Maybe there is something to enhance in QAP to avoid the issue, even if RestrictAnonymous is set to 1, but this is not of my "competency".... and I don't need it any more
PS : I also tried in the meantime to get help from ChatGPT, but if IA talked to me of this "restrictanonymous" registry value... it told me it was supposed to be in "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters".... We were "close" to the solution, but not in right place
PPS : What is strange also is that Windows GUI give an option to allow or disallow un-authentified sharing, but when allowed, miss to change also this registry value... that is not strictly andatory to access data, but is mandatory to access them in a "comfortable way".