Japanese maples are by nature woodland understory trees so all would prefer at least some shade...typically during the hottest part of the day. Yes, some can and will tolerate full sun but it is not their preference and their performance and appearance is often affected by that. And I would say that excess sun when leafing out is likely the cause of your maple's current appearance.

As to a cultivar ID, good luck!! There are just too many and with a similar appearance to be even remotely accurate. Even the JM authorities are reluctant to pin down an ID unless the tree is exhibiting characteristics that may be unique to that cultivar. And this one does not, sorry.

Thank you for your input.

Since it's not a typical leaf scorch I was thinking that maybe lack of water and too big roots were a cause of these burns as I suspect it wasnt getting enough water.

What other 3-4(5) meters tall maples would you say can tolerate most heat and sun? And if not many than what same height tree would work with a a Japan-ish style garden?

The straight species - Acer palmatum - Bloodgood, Emperor 1, Fire Glow and Sango Kaku can all tolerate full sun provided all other conditions (primarily adequate watering) are met. And most of the red laceleafs will as well, although unlikely to get to your height requirements. For whatever reason, the red foliage tends to be more sun tolerant than green, although may bronze out in very sunny conditions.

Thank you very much!

I will think what to do with the JM from the op and probably plant Sango Kaku or Emperor 1.

Have a good day <3