normally Desktop and Online are separate, but there's an offer this year to switch your desktop license to Online Premium Fed+State at no extra cost. The offer is displayed when you install the s/w on Win 10 (see below). But it's one way, if you do this you will no longer be able to use the desktop s/w, say to install on Win 11 later. I can't speak to the mechanics of how the offer is applied but think there is somewhere to enter your license code.
Online is not the same as Desktop - you're probably seeing that already if you got to the payment stage - no Forms mode, and you can only prepare 1 return. It's usually more expensive than desktop especially if you have multiple returns.
For more info on Desktop vs Online see comments from @VolvoGirl at the end of this thread
https://ttlc.intuit.com/community/taxes/discussion/re-you-can-t-compare-the-online-versions-a-rel-no...
More info:
https://ttlc.intuit.com/turbotax-support/en-us/help-article/download-products/end-support-windows-8-...
https://ttlc.intuit.com/turbotax-support/en-us/help-article/marketing/ty25-ttd-direct-offer/L0aUgksJ...
