@Daniel, I will continue here to not expand the number of threads.
I seem to have replaced all accounts in my flows. Now I have 3 flows where I use it and two more which are nearly empty (remnants of testing).
However I can not delete the old Gmail account. It is said to be used in one flow, which I can not find. Triple checked my three flows with Gmail and they all are switched to the new one. What makes me feel strange is that the new Gmail account is said (at the Accounts tab) to be used in 4 flows. I know there are only 3 where it is used now. There used to be 4th (where I tested it to let you know it works), but I deleted it.
Is it because the data is not yet updated or I miss something?