@GuWen, I've seen this warning after upgrading to Omada v6.  From a different thread, "Omada 6.x maintains full backward compatibility with all EAP models supported in Omada 5.x."  Regarding switches, it was a try it and see response and yours seems to be working.  (https://community.tp-link.com/en/business/forum/topic/848342)

I assume this is a warning you can ignore unless you're having problems, but it would be nice if it would go away unless there are firmware updates planned for the older devices.  My T1600G-28TS v3.0 didn't like the Omada V6 beta or initial release, but I tried again on my OC200 with the 2.22.10 Build 20251118 Rel.34511 release and no major issues since.