There’s a few UniFi 2.5G POE+ switches. But yes, it’s needed for the 6E APs as the UDM Pro does not have POE+. I’m not sure if POE+ injector would work as it may limit the transmission to 1G.
One practical consideration to note (other than pricing) is whether to go for fan or fanless (silent cooling) switches due to the noise.
Fanless and affordable (just for 6E AP) would be USW-Enterprise-8-PoE and optionally add a (Layer 2*) USW-Aggregation if more 10G ports is needed.
ONT > Gateway/Router (UDM Pro) > (using LAN SFP+) USW-Enterprise-8-PoE
@YongSG able to share ur WIFI 6 speeds with the U6 Enterprise on 2.5G?