On an unmodified (stock) Nintendo Switch, save data is encrypted and locked to your specific console and user account. You cannot simply copy a downloaded .dat or .sav file to your SD card and play it.
Finding a clean, uncorrupted save file requires using trusted community hubs. Avoid sketchy third-party blogs or ad-heavy download lockers that bundle malware with your files. The safest and most respected sources include: Pokemon Scarlet Save File Download
On the game’s Title Screen , press Up (D-pad) + B + X simultaneously. On an unmodified (stock) Nintendo Switch, save data