Why is my macOS Terminal is no longer recognising most common commands?

Feeling way out of my depth with this one. I have been trying to install Tartube to my MacOS via terminal. This involved installing Homebrew, Python 3, Gtk 3, Python Requests Module, Youtube-dl, the icons package mentioned, and FFmpeg. I was following the instructions on the GitHub page which was all going fine, until I finished the process and tried to run it, which returned a series of errors beyond my comprehension. I tried looking at what the troubleshooting options there were and first tried running

pip3 install PyGObject

Which made no difference, so I then tried running the troubleshooting option directly above that, which was to run these three lines:

echo "export PATH="python3 -m site --user-base/bin:$PATH"" >> ~/.zprofile
source ~/.zprofile
tartube

Since I did that, terminal no longer recognises most commands I run, including anything under brew. I tried reinstalling brew via the command line, but it returns an error saying it does not recognise “curl”. I reinstalled brew via the package, after which it started responding to brew commands, but after closing and reopening Terminal, that stopped working too. I have roughly deduced from some googling that it is something to do with $PATH, but I don’t particularly understand what most of it means. I’ve vaguely gathered that it could be to do with .zprofile and .bash_profile in the home folder, so I checked those and found neither existed. I’ve created both with what another question told me was the basics for those files, however it’s changed nothing. When I run

echo $PATH

All I get as returned is:

python3

When I open a new Terminal window, the following lines show before the input line, in case that’s important:

/Users/lucaquinn/.zprofile:export:6: not valid in this context: -m
/etc/zshrc:7: command not found: locale
/etc/zshrc_Apple_Terminal:104: command not found: mkdir