That sounds like a pretty good option, tho’ I’m not sure I could work out if the AW9523 is ok with sinking the current?
Another option is to just use less current on the LEDs! I was quite surprised to realise that the recommended max current on the LEDs has dropped from 25mA to 10mA (see Datasheet for LED Backlight is out-of-date - max current much lower?!). If I restrict myself to just 10mA per LED then the total draw would just be 160mA, which I guess is much lower than the 300mA limit on pin 3V3. I notice that the AW9523 also has an ISEL value in it’s Global Control Register that can be used to reduce the range of current emitted in constant-current mode (one of 25%, 50%, 75% or 100% of the 0-37mA range).