I'm not from Laminar Research, just a fellow simmer in the UK.
As you may have seen from this Q&A forum, there have been a great many other simmers who have reported this same problem, either when installing a digital download version, or when trying to install the DVD set.
1. In a vast number of cases, the problem has been related to anti virus software/firewall, although I note that you have already turned your anti virus software/firewall off which didn't help.
2. The other culprit could be a PC system specification that doesn't meet LR's minimum requirements, so please check here https://www.x-plane.com/kb/x-plane-11-system-requirements/
to make sure that your PC does?
3. LR recommends that XP11 is installed on your PC's desktop as opposed to a local hard drive, as this may overcome any 'permission' issues.
4. You may wish to try downloading the digital version in 'demo' format directly from LR's website to see if this works? If it does, then all you need to do to activate the 'demo' version, is to keep your DVD disk No 1 in the DVD ROM drive at all times.
Sorry, can't think of anything else currently, but hope this helps for now?