URL gives 404 error of my subfolder site when i change permalink

I have Created a subfolder site https://learnforget.com/hindi/, but in this, i am facing an issue. Url of the subfolder works fine when i use default url, but when i try to change my permalink to %postname% then its started giving 404 error. Here is also 2 problem occurs when i use same url as on my main site then my subfolder site url redirected to my main site url and when i use different url from main domain url then its giging 404 error eg.

https://learnforget.com/hindi/ amp
https://learnforget.com/ amp

In This case my subfolder url redirected to main domain url and in another case when url like

https://learnforget.com/hindi/ amp
https://learnforget.com/ ampos

In this case its giving 404 error