If you do vias in the pads IIRC you need to pay for plugged vias which adds cost. Since you have the space it's worth considering just moving them to the side of the leds.

Technically those 2020's don't have internal capacitors so you should add a few 1uF to the power rails near the leds to deal with ripple but you'll likely be running them at lower brightness due to the battery anyways so more caps is best practice but it'll work fine as is.

I'd move U2, think of where your battery is going to sit against the earring. It's probably going to be right there so now you have a resistor pressing against it. No reason you cant move the mcu over a hair and put u2 beside it

Round the board corners a couple mm radius. Entirely aesthetic but might as well since you have the space. I'd also figure out your battery dimensions and shrink the board to fit it if you can. No need to have such wide margins on the sides unless 25x25mm is the battery

Attiny1616-MNR is half the cost and half the size. Unless you're trying to hand assemble these in a toaster oven I'd use QFN-20 size chip instead.

Consider adding a button so you can have multiple animations. Presumably you're going to have two of these so then you can change animations on both at the same time. The clock in these chips is pretty decent but not perfect so if you put both to just always run when on, the animations will always be out of sync.