I have 4 Individual Estimated Income Tax vouchers for $2,400 each. Will I be fined if don't send any money to the IRS until April 15th, 2026?

IRS requires you to estimate your Required Annual Payment for the year and pay as you go.

you can base your estimate on prior year's tax , or 90% of this year's tax, whichever is smaller.
Each quarter your withholding and estimated tax paid must be at least 25% of the estimate, even if your income is uneven, [Otherwise, you will be penalized.] this is the simplified method, default.
if your estimate is based on this year's tax and turns out to be wrong you may be penalized.
you can compensate by overestimating.
if your estimate is based on prior year's tax, you know that when you file by April 15, which is also the first estimated tax payment due date. How convenient.

-----

Your own estimate may differ from the TurboTax estimate.

@pierre_morel