After checking the relevant information, I found out that this is actually a path setting problem. It is that your text actually exists, but the path you set is not correct causing the system to not find the requriements.txt file.
So, you just need to change your path setting to the path of the parent file you want to query.
I use the cmd system command cd to enter the specified file and then pip install -r requirments.txt method.
Example.
If requirements.txt is under the PythonProject file, then use
Cd C:\Users\xizhou\Desktop\PythonProject # Enter superior files first
pip install -r requirements.txt # Install pip again
The file can then be found.