How many leds can a arduino uno control?

[flashko]

Try the FAB_LED library.

GitHub - sonyhome/FAB_LED: Fast Arduino Bitbang LED library supports...

Highest number of WS2812 LEDs Uno can drive?

If you want to control an infinite number of LEDs with a UNO, you can't use the Adafruit library nor FastLEDs as they allocate 3 or 4 bytes per pixel to represent the strip in memory. HOWEVER you can use a library that can write on the fly the data to the pixels if you can do that with simple math, timing is limited (rainbow, simple color pattern etc.). For example I wrote FAB_LED on GitHub that allows you to do just that with an UNO or any other AVR microcontroller at 16MHz.