https://wccftech.com/nintendo-switch-system-update-6-1-0/

Nintendo has released Nintendo Switch System Update 6.1.0 which improves the system’s general stability and addresses an issue with Nintendo Switch Online.

Like previous Switch firmware updates, this new system update once again offers stability improvements to enhance user experience, but it also fixes an Switch Online issue where certain games don’t recognize a Nintendo Switch Online membership for a short time after purchase.