You can sell stock any day too, it's just not guaranteed you get out what you put in. What you needs is short-term bond so that you aren't stuck with the interest rate risk (when prevalent interest rate changes, your bond value changes too). Just to make a concrete example, if you buy VAB.TO in 2020, and you want your money now in 2024, you're currently down 20% from your purchase.

You need short-term bond (6-month, 1-month or even shorter) so that at worst you will get 100% of your money out by waiting for the maturity date. Money-market would be super short term: consider them as days-length bond.

But if we are talking about down payment money here, it's probably 100-200k something, which would translate to a few thousand dollars per year. Might not be worth your time, and definitely not worth it if you misunderstand and buy ETF bond or something like that. So yeah, keep it in a high-interest rate saving account is ok.