It has a Tools > Bootloader > No Bootloader option
If you insist on reinventing the wheel by making your own board definition, you will need to change the "uno" board identifier to something unique. You will also need to change upload.maximum_size to 32768 and bootloader.high_fuses to 0xDF.
Whether using MiniCore or your own board definitions, you must to a Tools > Burn Bootloader to disable the BOOTRST (boot reset vector) fuse.
The fuse change disables the boot reset vector, which means you can use the full flash memory for your application.
The Arduino IDE fails compilation (and thus the upload) if the sketch size exceeds upload.maximum_size. So by increasing this to 32 kB, the IDE will allow uploads of sketches that use up to the full flash capacity of the chip.
MiniCore also bundles an empty bootloader so that the Burn Bootloader command doesn't waste time flashing a bootloader that is not going to be used.
OK, well if you decide to give MiniCore another try, I'm sure we can help you fix the error, but we'd need the full error output. There are a near infinite number of possible causes of the generic "exit status 1".