Q.Outdoor Pot Plant
I’m looking to buy an outdoor pot plant to sit aside an LPG flue outlet. What do you recommend?

Certified GKH Gardening Expert
Unfortunately, I don't know of many that will tolerate that much carbon monoxide. If you plant, at least, a meter away then it might be fine, but I'd worry about dieback from the exhaust, still.
I know that this article isn't, exactly, on subject, but the plants recommended will tolerate the exhaust to some degree. These will be your best bet:
https://www.gardeningknowhow.com/garden-how-to/design/lideas/gardening-around-a-mailbox.htm