As shown here: Cubase 10.5 - Testing New Features & Discovering Bugs/Issues + Unpaid Review with Drama! - YouTube
Also, it is no longer possible to make things very dark grey or black. I made a Dark Theme preferences file here: Cubase 10 Dark Mode Theme , Free Instant Download! Which still ranks high on Google for Cubase 10 Dark Theme. It’s no longer possible to make Cubase look dark like this. You can only do a light-ish grey type of color. If you download the file linked in the article in 10.5 which is here Cubase Dark Mode Theme by Current Sound www.currentsound.com.zip — Yandex.Disk and load it into 10.5 Cubase it will cause the transparency issue as that is the exact file I am loading in the video. Even after loading it, setting to default as shown in the video did not work. I had to manually replace every single color and save a new preferences preset.