According to Classical Theravāda, the way Nibbāna is known is through path and fruition consciousness. Let’s skip the path consciousness because it only happens for a single mind-moment just before fruition consciousness. We will just talk about fruition. This is called phalasamāpatti. This is similar to a jhāna and Nibbāna is the object rather than a paṭibhāga-nimitta. This should be very clear. This is reflected in the extended Abhidhamma Citta list.
Once there is parinibbāna, there is no longer a citta. The five khandhas are extinguished with only dead matter remaining in the body. It is that simple.
If a Thai teacher teaches this, they have right view. I would suggest the teacher at Wat Khao Sanam Chai, in Hua Hin or similar teachers.
This is why we need Abhidhamma. The Thai teachers (Ajahn Brahm) you mentioned openly rejects the Abhidhamma.
Generally speaking, if a teacher rejects Abhidhamma, they are not considered to be of Classical Theravāda. We are not interested in anything else.