Thank you for your help.
On April 19th 2019 the Settings button disappeared from my Ubuntu 19.04. It was there previously. The settings button seems to have been replaced by the power button. I was able to change settings before, but now I'm not sure how I can do it.
Otherwise, the system is working without problems.
I'm a beginner in Linux. Should this be a bug report, or is there some way to get the button back?
Note: this post was originally written in Japanese and has been translated by humans. Misinterpretation may have occurred. Please see the revision history for the original text