After tax, I would still have more net income than before the raise...
This is almost always true, because only the portion of your income above the threshold for the higher bracket is taxed at the higher rate. The exceptions typically involve edge cases where additional income disallows some tax credit/deduction that isn't phased out.
How can I avoid income tax to the maximum possible?
Deductible/pre-tax retirement contributions, HSA, charitable giving, solar/ev tax credits, 529 plans in some states. Lots of resources on these, so wanted to focus on the other two points more.
Would gifting or
Gifting is not deductible. Charitable donations (to qualifying charities) are deductible. If you already itemize, then your federal tax saving is your marginal rate applied to the donated amount. If you're at 28%, then you give $1000 and pay $280 less income tax. This deduction caps at 50% of your adjusted gross income, less in some situations (related to nature of donations).
Or should I start employing negative gearing?
You could certainly do this, invest in some rental property that will generate paper losses thereby offsetting income tax burden. This is mostly kicking the tax-can down the road since depreciation will be recaptured, but it could work out nicely. There's always the risk of future tax-law changes so can't bank on long-term benefit, but short-term it can reduce income tax burden.
If you can buy a property that earns you more money, that seems better than losing money just to avoid taxes. In my opinion any scheme that results in losing money just to minimize income tax burden doesn't make sense when you could instead take the money you would have lost and given it to a charity. Charitable giving seems the best way to choose how your excess money gets used while reducing income tax burden.