>>53530310In generations 1 and 2 Pokemon Stadium served as the external Pokemon storage system. You could trade Pokemon between generations 1 and 2 via the Time Capsule, which emulated generation 1's systems.
The mechanics of the series were completely rebuilt for generation 3, and as such you couldn't transfer Pokemon from gen 2 up to gen 3. There the external storage system was Pokemon Box Ruby and Sapphire, a Gamecube game.
In generation 4, you could store Pokemon with the WiiWare game My Pokemon Ranch. WiiWare is long dead, so that game is abandonware. You could transfer Pokemon up from gen 3 to gen 4 via the DS's Dual Slot mode and the Pal Park ingame.
Generation 5 has no external storage system. You can transfer Pokemon from gen 4 to 5 using the Poke Transfer function, which requires two DS's.
Generation 6 has Pokemon Bank as its storage system. You can transfer Pokemon from gen 5 to 6 using the Poke Transporter app downloaded on 3DS after buying a Bank subscription. That's what's in danger today. The virtual console versions of gen 1 and 2 on 3DS can also send Pokemon to Bank, using the Transporter. This is the only official way to transfer Pokemon from gen 1/2 up to newer games.
Generation 7 also uses Pokemon Bank as its storage system. It works just like gen 6.
Generation 8 was moved to Switch, making Pokemon Home its external storage solution. Pokemon Bank can send Pokemon directly to Home.
Generation 9 will eventually get Home support, but for the moment it's not supported just yet.
So if you wanted to send your starter in Ruby up to use it in Scarlet, then you would go
>Dual Slot with Ruby and DPPt/HGSS using the Pal Park>Poke Transfer from say Diamond to Black 2>Poke Transporter from Black 2 to Pokemon Bank>Transfer from Pokemon Bank to Pokemon Home>Await Home support for Scarlet 
