Smooth rotary incremental encoders?

The clicks are called Detents. You are looking for encoders with 0 detent points, the Alps EC12E2430404 is one example.

Digikey has a whole range of detent-less rotary encoders

https://www.digikey.com/products/en/sensors-transducers/encoders/507?k=rotary+encoder&k=&pkeyword=rotary+encoder&pv1989=0&pv394=2&FV=ffe001fb&quantity=0&ColumnSort=0&page=1&stock=1&pageSize=25

In the case of the blue and metal 20-position rotary encoders widely available from Chinese resellers, you can actually convert the detented versions into non-detented versions.

Use needle-nose pliers to squeeze together each of the four split retaining clips (two on each side) holding the bottom and top halves together. Remove the top (metal-only) half. Use tweezers to remove the flat metal spring from that half and the tiny metal ball-bearing which creates the detent. Fit the two halves back together, re-spreading the retaining clips. And bingo, you've removed the detent-ness.