If it shows you version 17.2.1 then it's neither CS5 or CS6 but the latest version CC2022. CS referred to Creative Suite which were sold as perpetual licenses and have long been discontinued. The latest offering by Adobe is Creative Cloud i.e. CC, which is a subscription based software where you pay for the subscription and the updates are included in your subscription. The latest CC version for InDesign is currently CC2022 which is version 17 and that is what you seem to have.
You can find it alway on the Application Icon with right mouse click, at least oin the Mac > Information.
You can see it with any INDD file what version was used the last time (and all before) with which versions it was edited and saved: Hold down cmd/ctrl Key and go to the About InDesign… Menu (Mac under InDesign, Windows under Help), there is the document history where you find all informations about this file.