@donq
This solved my problem. Thanks a lot.

@gogoseit2020 The red icon appeared after an update of Opera,, not of Windows. So it seems unlikely to me that Windows should be the problem.

Since 2 updates ago the Opera icon on my toolbar turns red after downloading a file. It's not a file of a specific type.
With every update I hoped the problem would be gone. For me it is disturbing seeing that red icon. I hope there will be a solution soon.
I read on this forum that the same issue was posted in 2018 and solved, but is is back again.