With 300K of capital gains, you're gonna be in the 35% tax bracket if single, possibly the 32% bracket if married filing joint.
You do not need a 1040-ES to pay estimated taxes to the IRS. You can go online "right now" at www.irs.gov/payments and make a payment online. If you do, I would suggest you send the IRS no less than 35% of your gain, and you'll be good come tax filing time assuming you already have sufficient with holding on other income you receive during the year.
If your state also taxes personal income then I would suggest you also pay estimated taxes to your state, at whatever the highest rate is that your state taxes personal income. You'll have to check with your state department of revenue to see what your options are, as not all states that tax personal income offer the ability to pay on line.
Don't worry if you overpay your tax liability. At tax filing time any over payment will be refunded to you on your 2022 tax return.
