any idea if this exist ?
need to split or A/B the stick to 2 amps

HX Stomp

The StepAbout does this, and does it well.

An active solution is probably your best bet
but let's make sure we know exactly what we are trying to do
what modes of operation do you want?

I mean could you draw out the signal paths you want to accomplish? that could cut down on potential misunderstanding

[especially as "stereo" can get be little dangerously loaded term since the stick is technically dual mono...sometimes there can be hidden gotchas with that]

i just want , with a press of a button to switch between my bose s1 (that have both melody and bass inputs) and my (soon) spark can which also have those 2 inputs (and maybe play through both amps

Checking my understanding, I think you are looking for:

Stick Output Channel 1 => Bose Input Channel 1
Stick Output Channel 2 => Bose Input Channel 2

OR

Stick Output Channel 1 => Spark Input Channel 1
Stick Output Channel 2 => Spark Input Channel 2

And an ideal solution would also allow for:

Stick Output Channel 1 => Bose Input Channel 1 & Spark Input Channel 1
Stick Output Channel 2 => Bose Input Channel 2 & Spark Input Channel 2

Do I have that correct?

Edited to add 'Output Channel' & 'Input Channel' to clarify that there is just one Stick (with 2 outputs), and two amps, each with 2 inputs

nope.

one stick => 2 amps (each amp has 2 inputs)

In my illustration "1" & "2" are channels, not instruments, so I think that's what I illustrated?

The two channels of one Stick going to either or both of two amps (each of which can take two channels).

https://www.morleyproducts.com/gold-series-aby-mix/

this is mono-not stereo

mono is not a problem to find