You should first uninstall. Then, clean up all local settings.
It's a general problem for qt apps on windows , and I found a detailed description in Chinese:
https://blog.csdn.net/kenfan1647/article/details/121278742If you cannot follow, try to create a new windows user account, and try again.
Likely, your previous saved windows geometry was messed and saved, so reinstallation without cleaning up the user settings doesn't help.
Sandro wrote
I installed LibreCAD on an old Acer with Windows 7 and it runs regularly.
The problem seems to be in the computer. As soon as I can (a few weeks) I'll connect to the HP the second screen and try again.