Retirement tax questions

But isn’t it true that only 85% of social security income is considered taxable income? If so, then the total taxable income would fall under the 2025 Lon term capital gains tax rate of $48,350, which means zero capital gains tax, right? Even for vacation homes?  If so, great. In the same vein, what if the total taxable income for social security was, $50,000. Is  ALL of that subjected to CGT at 15%, or $1,650,the difference between  $50,000 and $48,350?