I tried that with robinhood, but that few minutes every month to dollar-cost average in + dealing with whole shares felt like a big distraction.

I switched to m1finance where you can set a "pie" e.g. 80% SPY, 20% bonds and then just add money. They do once-daily investing, and automatically add new money or dividends to even out the pie.

Now I once a month I just dump "extra" money in without needing to do any calculations.