I am an experienced english teacher, and yet I don't have a TEFL certification.Is it a must to have one, or there are exceptions ?
Welcome to the forum! For the positions you are having a look at, pay close attention to minimum requirements. If they require you to have an ESL certification, then yes, absolutely you need it. If it does not, having an ESL certification will be important to set you apart from other candidates and competition
I recommend you to have a look at the positions you are interested in, familiarize yourself with the requirements and apply to the ones that you are interested in
Good luck with your applications