Hello Chewy,
first of all, please accept my apologies for the issues caused by changing the Event Display options in Nuendo 10.1.
I have just learned that this is a side effect from merging the Cubase with the Nuendo codebases. The Event Display settings in Cubase used a different technology than the one Nuendo had been using for the last few years, and reportedly the older technology was starting to cause incompatibility issues on newer Operating Systems, which is why the newer Cubase settings (with many more display options) was imported into Nuendo.
Unfortunately Transparent Events was never an option in Cubase, thus the current situation. We are investigating the feasibility of implementing this as a new feature in an upcoming update, but it might take a while until it is back in Nuendo.
Again, I am very sorry and hope you can find a workaround to keep working with the current Nuendo version until we can offer you a better alternative.
All the best,