I have an ESP32 and it has GPIO 2, 4, 12-15 (six GPIOs) only.
My plan is to add a Nextion display and a ADS1115 (adc on I2C).
Do I have one more usable pin to ad a WS2811 light strip?
WS2811 is a 12V lightstrip, so you would need a controller for that and it is the interface on that you need to look at.
There are 4-7 volt versions also.
But some of these pins are said to have PWM at boot, I assume that won’t be a problem?
They only are PWM when told so in the software, and the one you like to use for the WS2811 well that is the simple FET schematic that all use to use the PWM from the ESP to control the led strip.