The most common problem I encounter is that signing into their email accounts. Google somehow decided to send prompt to the phone even though nothing has changed (same password, IP, computer, browser with cookies). And, my parents have no idea how to find the relevant notification and find the prompt. And, I even take some time because there're like a thousand notifications on their phones.
I tried to use the Find My Phone feature with my Samsung account a couple days ago. Log into Samsung with Google, on my friend's device as I've lost my phone, and Google says "we've sent a prompt to your phone to log in"... the phone that I'm trying to find. No alternative options, I just got frustrated and gave up and luckily found it on my own. Still not over how incredibly stupid that was.
As an alternative you could set up 2FA on their google accounts, and then they can have a 2FA app on their phone (not just google-authenticator, any app you trust can be good).
Then they would have a fixed place where they can find the 2FA code and not to mess around with the notifications. It's more complicated but more robust as well.
