I am looking for a VLAN aware access point.
I want to put IoT devices and normal devices to (at least) 2 different SSIDs. Though I don't want to isolate the IoT devices completely because some of them need access to specific resources in the main VLAN (e.g. a NAS).
I already have a pfSense router and a managed switch at home, so no routing/switching capability is needed.
From what I gathered, installing OpenWRT into a normal wireless router can make it VLAN aware (I hope I am correct).
The wireless router also need to support both 2.4ghz and 5ghz.
Is there any special hardware requirement for these features?
Or maybe I should just buy a real access point?
Yes! This is called a dumb access point. See the dumb ap wiki page where I linked some excellent videos and the rest of the page is a good reference as well.
VLAN, I believe anything that is supported by DSA or swconfig is VLAN aware.
SSIDs are software things, not hardware. You can have a single radio but multiple SSIDs.
Yes, you want a device with both radios (physical hardware).
No, not all of the 1,000+ supported devices support all three of these. A modern recommendation is the Belkin RT3200 which supports all 3 of your criteria, is WiFi6 (802.11ax), is well supported, and is under $100 at least in the US. There are many devices that will work though, that is just a single recommendation.