Executing machine code at runtime Uno
The microcontroller is executing one command at a time from..where?


Flash memory directly. The AVR core can only execute instructions from Flash memory. It uses a two-bus system known as Harvard Architecture, where the Instruction Bus is connected to Flash and is used to execute instructions, and the Data Bus is connected to SRAM, EEPROM, all the peripherals, GPIO pins, etc.

It is possible to jump to any location in memory in a similar way as you have depicted, but in order to know where you first need to know the functions you want to call.  You can get the address of any function and assign it to a pointer, and then call that pointer as a function, but what would that achieve? You may as well just call the function directly and save time. Unless you want to store the addresses of those functions in an array or something to maybe associate them with a command to trigger the execution of that function. In which case you don't need anything "fancy", just pointers to the functions you want to use.