The T4PS is the Statement of Employees Profit Sharing Plan Allocations and Payments. On it are things like capital gains/losses, dividends & foreign income. These are all things that are only available in TurboTax Premier Online (or higher) in 2021.

Please see these TurboTax FAQs for more information:

Why did I have to upgrade my TurboTax Online edition?

Who can file for free using TurboTax?

Why does my Spouse needs to pay higher amount for filing, too.  All he has is 1 T4, just because I have one T4PS slip from work, not a huge amount which I have it every year, now both of us has to pay the premium price of $39.95 each. Is there a way to avoid using & paying for Premier?

@Perlhume

If you prepare your return together with your spouse, then you will both will be using the same version of the program, and you will both be charged the same price. You can only prepare your returns in different products if you prepare your returns separately.