The new video does demonstrate your issue.

I've completed some research on the internet but unable to secure a solution. What happens if you uninstall Excel / Reboot / Then reinstall Excel ?

Thanks for doing some research as well!

I found the issue... I feel stupid, I had my monitor on higher contrast, instead of 50/100 it was on 65/100 (to help with visibility in my game). If I put it down like 3-4 points it already becomes visible again. Never thought that this would make such a difference :/

thx again though!