Putting this another way

Can I trade across platforms?

Yes, you are able to trade with players on different platforms (depending on those players’ Cross Platform settings). Trading will function the same as gifting, except for trading Platinum between Nintendo Switch and other platforms, which is not available.

To make sure you can trade with friends or fellow Tenno across platforms, make sure you are using a Cross Platform Save Account (or PC account*) and have Cross Platform Play enabled via your in-game settings. TennoGuard 2FA is required to trade in-game items with fellow Tenno in Warframe, which can be enabled via the Account Management page.

*PC accounts can automatically trade with players on other platforms — provided that both players still have Cross Platform Play enabled in their settings and that any non-PC player trading with them has a Cross Platform Save Account.

www.warframe.com/crossprogression

So rule 1: forget about Nintendo (Switch)

Rule 1: You can trade with anyone IF you and they have Cross-Save on their account.

No.

Simplest way to look at it: Warframe.com is the game, it is also on consoles.

PC is king in this realm. All those players are under his rule. They can trade with each other no problem, just have tennoguard turned on for each.

Consoles are kingdoms in the realm ruled by other entities than the KING. Little kings of various focus. Only some of the players there are Warframe players, and only some of them are cross-saved with the KING. Mostly they exists to commune in their little kingdom particularly. They trade with each other, may or may not have cross-play turned on, and it doesn’t matter, because Playstation is it’s own echo-sphere, for instance.

So players from the KING have cross-play on, they can also trade to consoles, as long as the console player has cross-save turned on for themselves, as well as cross-play.

Which leaves the little kingdom players in each place reduced in trading.

All sides think anyone can trade with anyone. Not true at all. PC can only trade with those who have signed up with the KING.

Those from Playstation that cross-save have put their allegiance to the KING, and are no longer privy to trading with their little kingdom.

Who loses out is the little kingdom dwellers.