I have hAP ax2 on the firs flor of my apartment. On the others flors WiFi speed is not perfect.
I have wires to other flors from the router. I'd like to buy couple more of hAP ax2 (or ax3 if I'll find any benefits over ax2) to connect it to the main one end extend WiFi network.

However, I'm slightly lost in technologies available in ax2. WiFi Wave2, CAPsMAN, MESH, etc. What should I use in order to have a kind of roaming across the apartment, when devices can hoping from one access point to another without loosing connection and manual switching of WiFi networks?

Roaming is a client thing, just make sure that SSID and all security settings are equal (and all devices are in the same L2 network.

Fyi:

• CAPsMAN is great fun, think it still lacks some functionality (but might be a bit complex to configure...learning curve is steep)
• Mesh is when you have a wireless backhaul...lucky you
• Wave2 is the only driver usable for this device...make sure it is installed