Unlike BBB, K3 only works with FAT, so create a normal fat32 partition, with at-least these 3 files:
├── tiboot3.bin
├── tispl.bin
└── u-boot.img
That’ll get you to u-boot prompt..
You can store anything else you want, i recommend the main kernel output files and go with extlinux.conf vs the old uEnv.txt..
Regards,