The output result of startOf ('day ') is incorrect

[orient-i]

Describe the bug
I am in the East Eighth District, and I have set my time zone to Etc/GMT (0) through the browser plugin "Change TimeZone". My current time is April 18, 2024 at 19:22. Here is the code and output result I entered in the official website console：

I want to know why the second console output is not 2024-04-18T00:00:00+00:00

To Reproduce
Steps to reproduce the behavior:

1. Install the plugin "Change TimeZone" on your Chrome browser
2. Enable plugins：

3. Enter code in the browser console

Expected behavior
the second console output is 2024-04-18T00:00:00+00:00