I got a Linux VM on my phone, on two of my laptops, run Arch on my main, installed Zorin on my wife's and my parent's notebooks and have Cachy on my PS4 and on my Switch.
Wait. In Denmark you are forced to either buy an iPhone or an Android for this "MitID" app!?
Is that app mandatory? Is it developed by the government?
If so, then being forced to buy one of these phones seems very wrong.
Depending on where you live, your friend might be eligible for using public transportation completely for free with a special id. It is also possible that their job security is going through the roof. One needs to be tested first, though and from what you wrote about them, I'd suggest that you or another person close to them escort them to a clinic. This way they don't get lost and can get help speaking with the personell when the instructions or other information get too complicated for them.
Just out of curiosity: What do you think 'll is the contraction of?