How can you run Genshin Impact in borderless windowed mode?

A non-Steam solution I've found:

1. Navigate to the C:\Program Files\Genshin Impact\Genshin Impact Game path and locate the GenshinImpact.exe executable.
2. Right-click to create a Shortcut to the executable.
3. Right-click the Shortcut to open its properties
4. In the Target field, append the string -popupwindow after whatever is currently inside the box.

5. Whenever you launch using the shortcut it should now start Genshin Impact in borderless windowed mode.

6. Make sure to press Alt + Enter when the game has launched.

This isn't available in the game to my knowledge, but there is a workaround that the community has found that may work for you. If you have Steam installed on your PC:

1. Open Steam.
2. Click "Games" in the top left corner, and in the submenu select "Add a Non-Steam Game."

3. A window will pop up, but don't select the game from there. Instead, click on "Browse."

4. Navigate to your Genshin Impact root folder. Find the "Genshin Impact Game" folder. Inside, select Genshinimpact.exe, then hit "Open" and hit "Add Selected Programs".
5. From your Steam library, right-click "GenshinImpact", then click "Browse."
6. Click "Set Launch Options" and add the line "-popupwindow." Hit "OK."
7. Launch the game. If it starts the game in fullscreen, hold Alt + Enter to set it to borderless window mode.

(Source)