So this one is pretty straight forward, I could not make my proxy work until I discovered that http is the default scheme in the proxy helper.

So the fix was very simple:

/usr/local/lib/python3.9/dist-packages/seleniumbase/core/proxy_helper.py
switch line 43 from:

""" scheme: "http",\n"""

to:
""" scheme: "https",\n"""

And it started working immediately:)

My suggestion: perhaps the scheme could be passed as a variable? Right now according to SeleniumBase documentation the correct format to add a proxy to your Chrome instance is: IP:Port:Username:Password
Perhaps it could be switched to Scheme://IP:Port:Username:Password?