@Alexandre. 

According to our knowledge base, the Deco BE65-PoE is equipped with 2 x 2.5GE (2.5 Gigabit Ethernet) ports. While the marketing materials may reference "5Gbps" to describe the combined theoretical bandwidth capability, the actual port speed specification is 2.5Gbps per port.

This means the Deco BE65-PoE will work perfectly with your 2.5Gbps TP-Link switch TL-SG108S-M2 for Ethernet backhaul, as the ports are natively 2.5Gbps capable. You'll be able to take full advantage of your 2.5Gbps network infrastructure.

  @Alexandre. 

The answer came from the tp-link knowledge data base I will have it corrected. According to this link https://www.tp-link.com/us/deco-mesh-wifi/product-family/deco-be65-poe/#overview

The ports are both 5 Gbps so either port will support 2.5 Gbps you just need to make sure your cables support that speed and your POE switch if your using one. 

  @Alexandre. 

Hi, 
@HelpFixDecoApp Thank you for your suggestion, and I agree with you that the ports on the Deco BE65-PoE are both 5 Gbps, so either port will support 2.5 Gbps when connected to the TP-Link switch TL-SG108S-M2 if the Ethernet cables also support that speed. (Note: the TL-SG108S-M2 is not a PoE switch.)

"According to our knowledge base, the Deco BE65-PoE is equipped with 2 x 2.5GE (2.5 Gigabit Ethernet) ports. "
- If this answer is from our live chat system, I have forwarded the information to the relevant team for correction. If this is from another system or website, could you please send us the link so we can correct it? Thanks!

Best Regards