My wife and I lived together for a bit back when we were dating. We did some math:
Combined rent + $savings = my old rent + her old rent
Then we split the combined rent roughly 1/3 - 2/3 (my salary was higher than hers at the time) so that we were both paying less than we had been before.
We split utilities 50/50 which was kind of a mistake IMO – I regret the accounting chore that it created. One of us would pay the rent by hand (USA, so paper check to the landlord), but utilities were on auto-pay from my account. We’d have to tally up utilities and add it or subtract it to the rent in order to reimburse the other person when they paid the rent.
Instead of that nonsense, I’d suggest estimating your utilities and split that figure 50/50 - then maybe look at it again once a year in case costs change.
Oh, I think that advice comes from a good place, it’s just misguided. People look at it and say “your partner shouldn’t be your cash cow”.
OTOH, I think it’s important for both people to be contributing to the household financially. That helps keep a certain balance in the relationship even if it’s just a token amount.
I think it’s more important that they come up with a system that they both think is fair. If moving in together leaves one person feeling like they’re being taken for a ride, it’ll wreck the relationship.