Downloading a "post-game" save file for Pokémon Scarlet or is difficult because Nintendo does not support cloud saves for main-series Pokémon titles. These files are locked to the internal memory of the console they were created on.
Downloading a Pokémon Scarlet save file from the internet is generally not possible for standard Nintendo Switch consoles because save data is stored directly on the system’s internal memory, not on the game cartridge or an external SD card. This design choice is intended to prevent data manipulation and cloning of Pokémon. Critical Save Data Information Pokemon Scarlet Save File Download
Emulators make it very simple to swap save files because they store data in standard Windows or Linux folders. Downloading a "post-game" save file for Pokémon Scarlet
Notes & rules:
For players looking for "completed" or "competitive" save files, community sites like Project Pokemon host files contributed by other users. What's included Replace the Save File: Downloading a Pokémon Scarlet