There's a lot of naughtiness out there.
I have a Wileyfox phone that was sold at a discount due to the Ad-X option. The Ad-X software is run by an organisation outside the UK and is not on the regisrar of Data Controllers.
A post-GDPR update initially required users to consent to the data collection before the adverts were displayed, obviously, I bypassed the consent each time as I was already fed up of seeing Deborah Meaden scowling at me whilst trying to sell me BitCoin investments. That worked for around a month until a futher update went through that forced consent and doesn't allow the withdrawal of consent.