1) You purchased $100 of SPY on June 15th, 2020

2) You're buying a house, and you need $100 today.

3) You sell $100 of SPY, and pay short-term capital gains (up to 37%)

OR...

1) You purchased $100 of SPY on June 15th, 2020

2) You're buying a house, and you need $100 today.

3) You take a loan for $100

4) You wait until June 15th, 2021 and then sell $100 of your SPY holdings, paying long-term capital gains (15-20%)

5) You repay the $100 loan

...it doesn't really avoid tax. It's just an alternative way of accessing capital by taking out a loan instead of liquidating assets.