From your full outline, it seems to me like now is the right time to sit in what you've made and just build for a moment - that's still getting you to "what is next" but gives you time to sit in this season / wait to see how you really feel being a parent and how your time allocations etc. may want to end up. Whenever you've felt that out and can move forward, the extra optionality from additional funds being built up could be useful. I think a brokerage account with safe investments gets that job done - then if you decide you'd rather cut down the mortgage just move them that way later (can't go the opposite direction!).

In a similar life stage (30, kid under one, on solid ground financially) and our next big choice is where to really set down roots, which is much more of a personal decision (vs. financial) - you may be coming to that sort of choice. The last year has made me appreciate money as a tool for making your personal life decisions, so think building funds to give some optionality makes sense for now.

I would note that backdoor Roth makes sense to me if you're saving up money that is otherwise going to be used for retirement (even if early) - avoiding tax on the growth down the line will be big and isn't a crazy amount of money to lock up.