One problem that comes up again and again is the seeming freezing or locking of the computer when adding a modification to the route in the FMC, like a direct-to on the LEGS page. Here is the solution. It is unlikely that we can fix this on our end, so I will pin this info.
What: When modding the ACTIVE route in the FMC, the framerate goes down and the computer does not respond fast, anymore.
Why: When the database for the navaids and fixes gets accessed, Windows Defender, Avast, and other anti-virus programs check the in- and out traffic for viruses. This slows the computer down a lot.
Solution: Create an exclusion in your antivirus program, excluding the X-Plane folder from instant checking.