Thanks for explaining more.
Are you using a programmable mouse or other kind of 3D controller plugged into your computer? If so, please try temporarily removing the device and try a standard mouse instead. This is worth a check because the unusual movement in the viewport may be being caused by your device not communicating correctly with iClone 8.
Do also check that you have the latest graphic drivers from Nvidia for the RTX 2080. If you are using the graphics drivers installed by Windows then they can already be out of date.
Finally, when you reinstalled iClone 8, did you download again or use the installer previously downloaded? If in doubt open up the Reallusion Hub Settings (top right cog icon) and click the Installer Location link. If the iClone 8 installer is there, please delete it and then download iClone 8 again.
Peter
Forum Administrator
www.reallusion.com