WLED has no Limit! i use 960x ws2812b with athom. 1024 leds is normaly max for 1 GPIO and 25 fps. this is a hardware limit of ws2812b... over 1024 the FPS will go down. i got 32fps with 960 leds. 44fps with 256 leds....
with 3000 leds at one gpio it could be 10fps or so. still enough for stripes but not for a matrix.
on a 3600 led matrix i use a diamex controller with 4x GPIO for leds.. 4x900 leds..