[Python] -bash: cannot execute: required file not found

I am having multiple problems with making my pythonscript dartsapp.py executable for my pi.

At first i tried to use

chmod +x dartsapp.py


and

./dartsapp.py


but i got the error:

-bash: ./dartsapp.py: cannot execute: required file not found


I also added the dir to PATH but still no luck. Afterwards i tried to use pyinstaller but when i try to call

pyinstaller --version


i get the same

-bash: pyinstaller: command not found


even though my PATH looks like this:

maxdu@LEDpi:~/0306 $ echo $PATH
/home/maxdu/0306:/home/maxdu/0306/dartsapp.py:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/local/games:/usr/games


What am i missing / doing wrong here?

Update:

ls -l /usr/bin/python3


gives me

lrwxrwxrwx 1 root root 10 Apr 9 2023 /usr/bin/python3 -> python3.11


and

head -n 3 dartsapp.py | cat -e


gives me

#!/usr/bin/python3^M$
^M$
# Python-App fM-CM-<r das PunktezM-CM-$hlen beim Darts^M$


and

type python3


gives me

python3 is hashed (/usr/bin/python3)

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