Asked and answered. Why did you change your user name? (Or this is one hell of a coincidence.)
https://ttlc.intuit.com/community/investments-and-rental-properties/discussion/re-sold-100-000-stock...
You owe the capital gains tax you owe. Period. The ideas to reduce your income tax are the same as for anyone else trying to reduce income tax. If you are due a bonus, see if it can be paid Jan 1 instead of Dec 31. If you are not already over the SALT cap for state and local income taxes and property taxes, you might prepay your 2021 property taxes if they are already assessed. (If taxes are legally assessed in 2020 and due payable in 2021, you can pay them in 2020 for a deduction. But if they are not legally assessed until 2021, you can't take a deduction in 2020 even if you pay them early.) Make a donation to charity (but then you can't spend the money yourself.)
You don't mention marital status or whether you are covered by a retirement plan at work. I'm guessing you are not married because if you were, you would not be over the Roth income limit.
If you are not covered by a retirement plan at work, you can contribute up to $6000 to a traditional IRA and get a tax deduction for it.
If you are covered by a retirement plan at work that allows you to make tax-free contributions (like a 401(k) or 403(b) then you could max out your contributions if you have not already done so. That's $19,500 if you are under age 50 and $26,000 if you are 50 or older. You can make up the lost take home pay by drawing out of the stock proceeds. That can be tax-free (a traditional 401(k) or after-tax (a "Roth 401(k)"). The regular method gets you a tax reduction in 2020, the Roth method does not save 2020 taxes but reduces your future taxes.
A backdoor Roth conversion saves you zero taxes this year, as already explained. If you are covered by a retirement plan at work and did not make contributions to an IRA, then you could contribute $6000 to an IRA that would be counted as non-deductible contributions, and then immediately roll that over to a Roth IRA. Because this is a non-deductible IRA contribution, it saves you nothing on tax in 2020. But it gets the money into a situation where (a) you can't spend the gains until you reach retirement age, but (b) when you reach retirement age, you can spend the gains without paying any more tax. You can gradually move your stock money into a Roth IRA at the rate of $6000 (or $7000) per year using this strategy.
If you are not covered by a retirement account at work, you can contribute $6000 to a traditional IRA, this will reduce your tax this year. If you covert it to a Roth, then you pay the tax that you were trying to avoid. This is not a backdoor conversion, it is just a regular conversion where you pay tax when you convert a deductible IRA to a Roth. If you contribute $6000 to a regular IRA, that's it for the year, you can't also do a "backdoor" Roth conversion because your overall limit to all IRA contributions is $6000 (or $7000 if you are over age 50).
If you have other non-taxed retirement assets, like a 401(k) or an IRA, you might go ahead and convert that now to a Roth account if you can. (You may not be able to convert a 401(k) if you are still employed with the plan sponsor.) Converting a regular 401(k) or IRA to a Roth account means paying all the income tax now (using the money in your stock fund) and then you never pay tax on that money again when you retire. That also does not reduce your 2020 tax (in fact, it increases it) but it lowers your future tax.
You might buy tax-free muni bonds, but again, that reduces your future tax, not your 2020 tax.
You should probably consult a professional tax advisor.
