Online tax software for 2023 or earlier years is permanently closed; online for 2024 has not yet opened--that may occur within a few weeks from now.
You can use online (when it becomes available) to prepare a tax return and file by mail if you want to---but you still have to pay for using the software. The fee for using online is the same whether you e-file or file by mailing the return in an envelope.
The IRS will not begin to accept 2024 returns until sometime in late January 2025.