Syncing gmail across devices

A while back someone raised the following problem: "..., my Gmail account that I access using Mac Mail quit syncing with my iPhone. If I delete a message on my phone, it will not delete on my Macbook Pro. I have no problems receiving mail on either device. If I delete a gmail from Mac Mail on my Macbook, it does delete on my phone. Seems to only have issues one direction, when I delete on my phone. It's just not detecting that on my MacBook. Thank you for your help." I am experiencing the exact same problem and could not find the advice given for this question. (I'm a bit of a technophobe retiree so need fairly detailed and basic instructions. 😂) Many thanks!