Really? Oh thats interesting.
Thank you, but if you want to support it you need to hit the vote button in the upper left! 
Same issue here. Had the problem with Cubase 12 Pro and Cubase 13 Pro with a brand new project file. Beginning it was working, now just stopped I don’t know why.
Hi,
This is a known issue in Cubase 13. If a Ruler track is in the project, the Insert Silence doesn’t work as expected.
This is going to be fixed in the 1st maintenance update.
Thanks, that was it! I have for every project a timecode ruler with the time stamp on the top.
I can confirm, removing the ruler bar gives the insert function back.
Deleting is possible even with the ruler.
Will it be corrected in the next Update?