My worst interview experience was when the interviewer asked an IQ question, something about filling a few bottles

I panicked and didnt have time to think thru.

Long story short, i didnt get that job.

During the interview i panicked because i was trying to give a quick answer.

But it took me awhile to figure out the answer after that. This was a story 10 years ago when i was a fresh grad.

You can ask several pressing questions about the work itself to show your interest for the position(i list the question in general):

a) what is the current goal/ direction of the department?

b) what are the challenges faced by the current department?

c) how will my role fit into helping the team to achieve the goal?

Always ask question about your job scope rather than asking about monetary benefits. You can ask that once you are offered the position.
I notice asking too much on monetary benefits somehow turn off the interviewer.

hi, im not sure about what job are you looking for but for me as engineer, professional and academic certs are important.

event participation (uni events, outside events) certs are negligible unless they are career course related.

probably you should ask the HR if the certs are relevant to be shared in the interview?

no need for thank you note. i think it is practically useless in malaysia.

a good and honest interview will be enough to give good impression to the hiring manager.