Does TT Online allow capital loss carryover to be used to offset unlimited capital gains? I don't see that option.

For a capital loss carryover -

Click on Federal Taxes (Personal using Home and Business)
Click on Wages and Income (Personal Income using Home and Business)
Click on I'll choose what I work on (if shown)
Under Investment Income
On Capital Loss Carryover, click the start or update button

In order to enter a capital loss carryover in TurboTax Online you have to be using the Premium edition.

There are no options in the tax law for how a capital loss carryover offsets capital gains. Enter the capital loss carryover in TurboTax. TurboTax will use it as specified by the tax laws.

I'm not sure what you mean by "unlimited capital gains." There is no limit to how much gain can by offset by a capital loss carryover. If your net capital gain in 2024 is more than the capital loss carryover, the entire capital loss carryover will be used to offset capital gains.

You get to first offset the loss against any gains you have each year so that can use more of it up. Then after applying the loss to the current gains if there is still a loss, you can take a max loss of 3,000 per year.

On the income page The 2024 column shows the carryover to 2025 (not your current loss for 2024). Schedule D doesn't actually show the carryover amount. To find your Capital Loss Carryover amount you need to look at your return schedule D page 2. Line 16 will be your total loss and line 21 should be a max loss of 3,000. The difference between line 16 and 21 is the carryover loss for next year.

Then there are 2 worksheets….
Capital Loss Carryover worksheet showing the carryover from the prior year and the current amounts.
Capital Loss Carry Forward worksheet showing the amount transferring over to next year.

In the Online version you have to save your return with all the worksheets as a pdf file to your computer to see the Capital Loss worksheets. You need to use Online Premium to enter a Capital Loss Carryover and investments. Or any of the Desktop programs. In the Desktop program you can switch to Forms Mode and open the worksheets.