At least 6.2.9 has 210B listed in "config wireless-controller wpt-profile". I would try upgrade the 210B to the latest as possible, then try with 6.2.x FortiGate. But of course, it's time to invest money for better WiFi security&performance.
I cannot see the Ap firmware of the fortiap 210B on 5.4 just on 5.2 xD
I cannot see it on 6.2 either.
I know its time to invest on new hardware, but i dont know why this old ap has support until 2023. I just find it really odd. I want this client to change their old hardware but i just want to list like all the reason of why they should.
And i was wondering if having the AP with an older firmware than the fortigate could make it act weird or if its supported.( like i said, i cannot see that firmware to download on the fortinet support site)
Many FGTs in the world still run with 5.6 or even older. So as its peripherals.
Of course, the FortiOS 6.2 release notes say "FortiAP 5.4.2 and later" in integration section. But since the 210B is still in the profile list, it has a chance it might work even it has 5.2x. That's all I'm saying.
B series doesn't support 802.11ac or later technology, of course including the latest 802.11ax/WiFi 6 and WPA3. I don't think it would support channel bonding like 40MHz. We still have 221B with FAP's 5.4.x. But about to get rid of while we have 221Cs, 221Es in the mix.