Is it compulsory to have the yellow fever vaccination for entry into Thailand from Nigeria?

Assuming you're Nigerian and the Nigerian authorities don't impose a yellow fever vaccination requirement on their citizens to leave the country (many African countries do) then you first have to find a country that doesn't require the shot to enter or transit (such as European countries) before flying to Thailand.

However, that isn't a guarantee because Thai immigration still pulls aside all Nigerian nationals to check their yellow fever vaccination certificate.

In theory, a minimum 10 day stay in a non-yellow fever country should negate this requirement, but it's uncharted waters.

If you're concerned, you might want to consider getting a "contraindication to vaccination certificate ".

I don't know if the Thai authorities will accept this for quarantine free entry.

Singapore imposes a 6-day quarantine on holders of this certificate (meaning anyone who is medically unfit to be vaccinated against yellow fever) and I suspect the Thais are the same but I don't know for sure.

No, they just take everyone from that plane to the side and you have to fill in an extra form (you get put into some online system). In theory you are meant to then log in after I think 5-7 days and tick a box that says you are symptomless, but I forgot and nothing happened.

Yes. You need to fill out the T.8 Thailand Health Pass otherwise you won't be issued a boarding pass.

You might get denied entry even in the connection countries. Get the vaccine, come on!

If you don't have it and you travel from a country that has Yellow Fever you will likely be denied entry

Yes