@Somnus 

Thanks for your answer !  

But, discovering the world of routers and Omada, i saw that my vDSL box can't work as a "Bridge" (it's a simple user adsl box from the french Orange network, the bridge option is impossible)

I will be obliged to have the router of my vDSL box and the router OMADA 605

So, can i connect the OMADA Router behind this vDSL box like this :

- the vDSL box will keep its original adress   192.168.1.1  /   2555.255.255.0

- I assign  192.168.1.2  for the WAN side of the OMADA  ER605 (connected to my vDSL Box)

- I assign  192.168.2.1  for the LAN side of the OMADA  ER605

I will have 2 networks  : 

Box 192.168.1.1  (only to connect Omada ER605)

Omada  192.168.2.1     

And then with the VLANs   192.168.20.1  for Connected objects         192.168.30.1   for Pcs     192.168.40.1   for Guest

Sorry for bad english.

I don't want you to give me the complete solution, i just want to know if it's possible to do this kind of project, with a vDSL box who can't work in Bridge mode.

Thank you.

  @Somnus 

Thanks twice !

I've read something like that about double NAT.... Anyway, it's very interesting.  And There is always a solution.

My first goal is to disconnect  domotic objects (Tuya, Hue, Amazon ) from my principal computer and laptop in the Network.  It's the reason why i need to buy something like ER605 and WiFi access Point from TPLINK.

Perhaps i will connect my game console directly to the vDSL Router box  as it is today...  there is no sensible datas in a game console.

I will see for the next steps . The best thing is that you said me it's possible to start with ER605 alone !  because i was almost sure it needed an Omada switch from the start.

Have a good day @Somnus   

J-Ch.