The thread pattern is hard to match. for my truck i ended up using an oil plug for a BMW motorcycle as nothing else would fit right.

you could also plug it with an old O2 sensor from a junk yard.

EHHH Wrong not a smart idea, you better not do that unless you want screw something up, and besides the check engine light will still stay on.

you should be fine unless you don’t plug it tight enough. The car was built to have only 2 sensors in the first place.

If the car’s control module expects only two, you may plug the port without a problem. Usually a standard bolt does not have the same threads.