Unable to execute shebang scripts after chmod +x

That #!/usr/local/bin<space>python3 is an incorrect invocation. As there is no python3 installed by Apple, you can use either of the following:

#!/usr/local/env python3

or

#!/usr/local/bin/python3

The latter would simply be a link into the Python3 framework that is likely installed in Library/Frameworks.

I believe that noexec option in the mounted filesystem will halt any attempt to execute code on it.

This is not exclusive to you. 😉

That space in your python3 invocation line should have complained:

Is it the script itself that won't run, or just some of its statements? Was your system updated after the reset?