Using Treasury ETFs Within Taxable as an "Envelope" System?

I've taken to using SGOV within my taxable account to save money for a car downpayment. Though as time goes on, I invariably have new and upcoming goals/necessities, though I have a predisposition to the need to compartmentalize everything in my life.

Does anyone at all use ETFs similar to SGOV (or caution/advise against this with reason) as a way to visualize the different goals for which each ETF is assigned to?

Taking cues from the envelope system where people will allocate any given amount of money for a specific budget list item and place it in an envelope to separate it from the other money/avoid mixing.