Hi, am about to apply for citizenship, I spent the entire year of 2020 living in Ireland. I presume I wouldn't have had to file taxes in Canada for 2020? I presume you only tick the boxes that you lived and worked in Canada.
For citizenship, you only have to file for a certain number of years in the preceding 5, not all years. That is a specific requirement and the only thing IRCC will look for. You have an obligation to file tax returns, but you do not have to report anything or any changes to the IRCC. Indeed, IRCC will require you permission to see if you have indeed filed returns as per the requirements for citizenship, which permission you would presumably give them anyway.
I don't want to presume any lack of awareness on you part, but I should note a confusion that many seem to run into---that filing tax returns in Canada is quite different from actually paying taxes in Canada. If the country has a tax agreement with Canada (and Ireland most likely has), then you can file as a "deemed resident" ... not easy to explain, but roughly, you pay taxes in that other country and also file in Canada ... but only for tax purposes (not immigration etc.) you are considered to be a resident of Canada. In short, you can file just to say "I an filing and I owe nothing".
As for "only tick the boxes that you lived and worked in Canada", I suggest you provide whatever information is required. For sure, if you "spent the entire year of 2020 living in Ireland", then it will have to show up somewhere in the information you provide, or you will be asked about it when the "residency" part of your application is examined.