If you have switch v1 (old model) then it's very easy. You just have to install software mod (Hekate and Atmosphere) by following tutorials on YouTube.

If you have switch v2/oled/lite then you have to buy picofly mod chip and solder it on your switch. And then you install Hekate and Atmosphere.

I got a guy in a video game store to do it for $70 (Picofly Chip + Soldering + Installing Mod Files).

Since then I have probably played 100s of games for free, on my switch.