If you don’t need to use video in Cubase you could remove the videoengine components from the components folder.
If you need video then try updating graphics drivers and quicktime.
As for the system link…I’ve never even noticed this flashing by on initialisation…are you actually using it?
If not make sure it’s not enabled in Device setup.
Other than that you could try running in safe mode
https://www.steinberg.net/en/support/knowledgebase_new/show_details/kb_show/safe-start-mode-resetting-the-cubase-preferences/kb_back/2020.html?tx_p77sbknowledgebase_pi1
& If it runs better this way, you’ll need to permanently trash your preferences.