Could someone try to merge no outlines with 100% catch rate (it might worke) and generate the ips? (ips patches https://gbatemp.net/threads/batch-tool-to-generate-ips-patches-for-pkmn-su-mo.452178/)
I have the same problem since few days. And I think it is a problem with system/update(?). On my laptop I was able to upload .hex without a problem.
/EDIT
Be sure that you are selecting a good hex file.
Everything else is OK.
UNO R3 like this (microUSB) will also works: https://www.aliexpress.com/item/1pcs-New-2016-UNO-R3-ATmega328P-CH340G-MicroUSB-Compatible-for-Arduino-UNO-Rev-3-0-hei/32689124737.html
Change the name of arm9loaderhax.bin from BootAnime9.zip to arm9leaderhax_si.bin and put it to the root of the SD card. Also put the arm9loaderhax.bin from Luma3DSv6.6.7z (important) to /anim/ and change the name to arm9payload.bin
For some reason the latest arm9loaderhax.bin from LumaUpdater...
Save backup manager.
1. Running application with additional button (for ex: A) will run home menu.
2. Select applications and games to backup (with checkbox).
3. Save selection. Exit app.
4. Run application without additional button will create backup on SD card of selected programs and games...