Honestly though they transform so close to other people. In Jackady/SimonSayz when Adrien ducked into his bathroom to 'shower' I bet Nino was just standing outside shaking his head in shame. He can literally hear the bloody theme music and see the sparkles coming out from under the door, let alone not notice the yell of 'Plagg, transform me!' I like to think Nino spent most of that episode trying not to laugh as he watched Adrien make poor excuses just so he could run off and do his magical girl transformation with accompanying music.
While rewatching Miraculous Ladybug today I realised how poorly the children hide when they transform. Marinette jumped behind a wooden bench in a public park right by a fence in Climatika??? That’s not very genius hiding.
Now I’m all for the head cannon that the Miraculous have glamours to hide their identity, but I also like the idea of a Danny Phantom kind of scenario. Like literally every civilian KNOWS who Ladybug and Chat Noir are because they’ve seen them transform right in front of them when the kids think they’re hiding so cleverly in bloody plain sight on the street and just outside class.
However they don’t have the heart to tell the kids that they know as they try so hard to keep their identities hidden (it’s not their fault they’re not very aware of their surroundings), so instead everyone just…pretends they don’t know.
Shop owners will give Adrien and Marinette free products when they realise who they are, but Adrien waves them off as part of being famous and Marinette is too sweet to not believe their excuses of there being extra stock. Their teachers even give them slack when they come in with bags under their eyes after a late night of chasing an akuma.
Alya directs outsiders and tourists away from their identities by feeding the Lasyblog false information. The Parisians are very protective of their heroes.
So basically we just see the series from Marinette and occasionally Adrian’s view, in which they keep their identity safe. Meanwhile everyone around them are trying their best to support the two young teens as discreetly as possible.