Remove blog from permalink in WPMU main site?

i have wordpress MU, everything is fine in child sites , but in the main site in the permalink structure have been changed itself , mean that after the site url it have like https://example.com/blog ,

most probably this is the site url, i have checked this in my db it still like https://example.com/ , what is wrong with my WPMU? have any guess ? i have followed everything in other posts like WPMU developers and so on , but no luck,

Also when, i have to go single page, it redirects into me on home page, so that i decided , this is the problem

check my attached screenshot for more details : https://i.stack.imgur.com/HvOUJ.png