Having issue 404 not found in subfolder installation

Hi guys,

Recently I got the issue as the title. Here is the detail.

I have wordpress installed in my domain (let’s say Az ) , and it’s in root folder, this installation is single site not multisite.
And I was uploading another wordpress (let’s say Bz) , which is single site installation not a multisite , to subfolder.

After connecting with database , I can access the Bz , but all of them not found , the post , the page , even the /wp-admin/ in Bz is not found.

Is there some conflict between Az’s and Bz’s .htaccess ?
So any idea for this?
Fyi , I already edit the .htaccess for Bz

Thank you