I’ve found the thread, and this is an extract from the OP.
In recent months there has been increasing interest and chat around the concept of 15 minute cities. My understanding of the scheme is that within your own city zone, all your requirements for shops, education, health, recreation etc. will be available. Travel outside your zone on foot, public transport, cycle etc. will be allowed. However you would not be able to use your car more than 100 times per year to leave your zone to go into or cross another zone. To keep control of the use of cars, recognition cameras would monitor vehicle and fines issued to people who use their car to cross zones more than the allotted number of times. There would be exemptions for certain vehicles.
That may or may not be an accurate description of what was intended, but it is the last part of the extract that I objected to. Fining people who cross zones is another way to exercise social control, with more freedom for those who can afford to pay. As with ULEZ, it imposes huge restrictions on those unable to walk or cycle, and who have poor public transport facilities.
By all means, give people the ability to access basics without having to travel, and provide public transport for when they need or want to, but ghettoising them and containing them in zones is dystopian IMO, and it is made worse by allowing those who wish to escape their (probably much nicer) areas the right to do so if they pay a ‘fine’ (aka a mobility tax) to do so.