I have a 12 year old DS who I am happy to leave pretty much all day - he is really sensible, good at checking in and always answers phone, updates on where he's going and also has Apple find iPhone enabled for emergency's. In the holidays he will go to goals to play football for 5/6 hours at a time, walk himself back, manages himself at school all day and takes himself there and back. I wouldn't be comfortable him waking up alone or going to bed alone though or doing mealtimes - I normally give him money for lunch if he's going out or would pop back to give him lunch or leave him something.
I'll leave my 10 year old with him for around 2/3 hours tops and only if I'm going somewhere close by. Normally popping into town to the shops/ foodshop etc. wouldn't leave my 10 year old longer than an hour alone if I am again local and could get back within 15 mins. He also has a phone and could contact me etc.
I also have an 8 year old I would leave for 20 mins with the boys if say I was going to the local tescos 5 mins away to grab something although would never leave her alone. She also has an iPad so she could contact and knows how to if needs be.
I am a single mum so I have had to do this a bit earlier than I probably would have otherwise, covid when you couldn't take the children into the shop, or I thought it was safer to leave them for 10 mins than to take them out the house. I also have neighbours both sides who the kids know they could go to - they have my phone number, their dad lives literally round the corner, my other family members also in the same town only 5 min drive away. I also have a dog which makes me a bit safer leaving them. (Although she's locked in kitchen when I'm out) but think people less likely to intrude.
I've never had a problem they are generally watching tv or on PlayStations anyway and are exactly where I leave them 😂
I'll probably get flamed for this now but I am comfortable and the kids are comfortable and if ever we weren't then we would change it.