Error on running the Flask UI with Python 3

While working with Python 3 (version 3.9.1 on my local machine) and checking out to feature/python3.8 branch the following error occurs when trying to run the Flask UI:

File "/path/to/PortScanner/src/mainScanner.py", line 10, in <module>
    from multi.scanner_thread import split_processing
ImportError: bad magic number in 'multi': b'\x03\xf3\r\n'

I am assuming this is caused due to using more recent Python 3 version than the one specified in README.md.

Mentioning @Kashish121 as stated by @vinitshahdeo.

Originally this issue was discussed here.