I've tried to insert an SVG logo and THE SITE IS CRASHED!!!
1)WP can't let me to upload an SVG file so i've upload it via FTP.
2)Site is totally crashed.
3)I've delete the SVG file by Upload Folder.
4)Site is still OFF
Any suggests? That's only a coincidence?
Hard to tell what happened without an error log from your server. You will have dig into your server or ask your hosting provider about this.
You can also follow this article https://themeisle.com/blog/wordpress-error-log-debug/
To use SVG in WordPress you need plugin like explained here https://rifetheme.com/apollo13-framework/docs/customizing-the-theme/header/svg-logo/
With kind regards.