Can I enter Thailand with a Canadian passport valid for 4 months and 20 days?

No

No

All it would take is suspended flights due to any kind of conflict. I got stuck in saudi for 8 months during covid.

No...

If you use this IATA tool you can see that the passport must be valid for the period of stay. So the rule of 6 months is simply not true.

The big issue is to explain it at the airline desk when you check in.

I would not travel anywhere with less than 6 months left, you are talking a chance that I would not take.

Go with agency. But seriously i suggest to renew it.

Okay. So this is slightly complicated, and I'll tell you right now that you are going to get a LOT of wrong answers. 99% of people are going to say "NO YOU CANNOT TRAVEL WITH LESS THAN 6 MONTHS!!!!!!!!!!!!!" but they are not correct.

Thailand has NO rule that requires 6 months of passport validity to enter. The only 6 month rule that Thailand has, is that embassies require 6 months of passport validity to apply for a visa.

The ACTUAL rule for entering Thailand is that your passport must be valid for as long as you will be stamped in for. So if you arrived today without a visa, which means you will receive a 60 day visa exempt stamp, and your passport was valid for 4 months, you are completely fine. You will receive your 60 day stamp and be on your way.

However if you arrived and you only had 50 days left, you would not be okay because your passport is not valid long enough for your entry stamp.

BUT here is the problem. Airline staff around the world are trained to not let people fly with passports less than 6 months validity. That's because MOST countries do not allow you to enter if your passport is valid less than that. So out of hand, airline staff will reject you. You will have an uphill battle convincing them that you will be fine once you arrive to Thailand, and will be able to enter. So I highly recommend you renew your passport before traveling. Else you stand a good chance of being denied by the airline. But if you can make it to Thailand, they'll let you in.

Most, if not all, airlines won’t let you board. You can get a Canadian passport with urgent pick-up (by the end of next business day) or express pick-up (2 to 9 business days).

Nope highly unlikely airline will let you board