Ok, do this:
1) On Universal Updater download the Vapecord plugin. Reboot the console, open Rosalina and set Plugin Loader to ENABLED.
2) Copy the sav file to the game's folder (aka the first thing you tried)
3) Follow the steps Vapecord tells you, and backup you garden_plus.dat file.
4) Close...
I think it would be easier to make a NAND backup on the old one and restoring it on the new one. After that put the sdcard of the old console in the new one
btw i feel this a good time to remind you guys that sea of thieves was made by rare, who also made DKC1-3 and DK64, alongside banjo kazooie and conker's bad fur day