Guessing that you have already expanded your Freighter with bulkhead upgrades to increase the amount of slots.

The upgrades you are trying to install should go in either your Freighters General inventory, or the Technology inventory, and have synergy bonuses for installing them next to each other. Just like any other upgrades you can have three in each inventory of each type, things get a bit tight in the Tech inventory so you have to prioritise what you want in there.

Why they are not in your case is unusual.

Maybe you need to have a few fleet rooms and frigates first? (I have always had these before getting Freighter upgrades from the derelict freighters). If you already have them, maybe you have mods installed causing problems? .. honestly I have no clue.

Lucky you getting S Class, very weird you cant install them.

Edit : There's a topic on reddit which a few people are saying the Expeditions reward for these are buggy, %NAME% should be the name of the Derelict you get them from, maybe Hellogames didn't validate these rewarded upgrades correctly? .. https://www.reddit.com/r/NoMansSkyTheGame/comments/mlc5jx/no_mans_sky_cant_install_salvaged_fleet_unit/