With all due respect, I welded an exhaust extendion and placed it
through an airtight seal to the window.

Homemade welds and seals, sure, that's safe....

Have you ever been inside a commercial repair facility that pipes the
auto exhausts to the vehicles they are working on?

Which often have a good bit of OTHER air circulation equipment. Unlike a
residential garage that typically has NONE.

BTW My last condo had a humongeous diesel generator for emergency power
located inside our 21 story building. Our unit was next to it. It was
exhausted to the outside. You have to know what you are doing to be
safe.

A professionally installed and inspected setup is one thing, your's isn't.
You can't compare them.

Generically, you are correct. BUT! Under the conditions that I
described, not a problem.

Sez who?

I also use a CO2 detector.

Which will do no good whatsoever. You need to be monitoring for carbon
MONOXIDE (CO), not simply carbon DIOXIDE (co2). Likewise they need to be
mounted properly and in locations best suited for safety. One in the
bedroom is a LOT more valuable in than one mounted too low in the garage.