macOS Big Sur brings a lot of interesting tweaking options to Safari. Now, you can change the look of Safari according to your work style and personal preferences. You can tweak a lot of things from changing the startup page background image to adjusting your favorite website list, Siri suggestions, reading list, iCloud tabs, etc.
The following is a detailed guide on how to change the background of Safari boot page on macOS Big Sur.
Step 1: Open Safari on your Mac and press the bar button at the bottom right corner of the start page.
Step 2: From the menu that opens, you can choose the wallpaper from the list provided by Apple or click the plus button to select the wallpaper you save on your computer.
Step 3: Browse and select the image you want to set as the startup page of Safari.
Step 4: Click on the image to preview the result.
Step 5: When you're satisfied, click the Choose button to confirm.
Note: When you want to change to another wallpaper, you need to delete the current wallpaper first. Open Safari's launch page> click the horizontal bar button in the lower right corner> click the X button located in the upper left corner of the background image you want to delete> click the plus button to select a new background image.
If you do not want to set the background image for the Safari start page, you can disable this setting, open Safari> click the three bar buttons> uncheck the Background Image option.