These generic Chinese ESC uses the cheapest but reliable RU6888R. During my ebikes days, we use to mods these by changing the mosfets, higher value resistor for the regulator & modify the shunt. These Chinese ESC doesn’t have the shunts, may be they are software based, i donno.
RED circle is the 7815 regulator. If you do plan to over volt it then just add a 470 ohm resistor before the input to lower down the input voltage. A watt will do, i think, if its really hot then increase to 2 or 3 watt resistor.
For ebikes, we use to replace these with FDP2532 as it was the best & cheap at that time. You’ll need the 100 volt cap for these upgrades. It is a good idea to upgrade the heatsink as well. You can salvage it from a dead PC PSU, most of them are about the same size. After that, you should be able to use 12S, 13S, 16S or may be even 20S !
But who would dare to ride on a 20S, safety first in case you really do plan to do these upgrades !