I've been thinking about this and realized this was only ever a notice from my tax software and not something that the CRA ever mentioned, and frankly I have been making "installment" payments throughout 2020 through my paycheques at work. I've ended up owing a bit at the end of the year through a combination of bonuses, consulting income, and dividends, but the majority of my tax bill is paid by the end of the year.
I think I've just about convinced myself this isn't a big deal, but please let me know if you think differently ;) I just hated the thought of a penalty for something I was willing to do, but never was prompted for!