Claiming the hardware or unit as a whole isnt their responsibility is a pretty brazen false claim, especially considering its their manufacturer's warranty that covers the device - not Roku's.
What's even stranger is that you are inclined to agree with them. Roku did not make your TV - it did not manufacture the constituent physical components nor assemble them.
Roku's entire contribution is licensing the RokuOS software to the (unknown) manufacturer.
WiFi Certification involves hardware products - not software (e.g. Microsoft Windows is not WiFi Certified).
WPA3 (a WiFi Allliance standard) is a requirement for WiFi certification as of July 2020 (and optional prior to then), but Roku doesnt WiFi certify their products (nor do their competitors), so they dont have any real impetus to include WPA3 support (nor do their competitors).
Regardless, since Roku doesnt make Roku TVs (the manufacturers do) and since WiFi certification only certifies hardware units, the Roku TV manufacturer would have to certify their TVs (and thus have to meet WPA3 certification requirements).
So if a product isnt WiFi certified, WPA3 support is entirely "optional" (discretion of the manufacturer), which is (one reason) why so many products are still sold without it.
Yes, Roku would have to provide OS-level support, but since they dont WiFi certify their products, there is no rush to include the support (a Roku TV manufacturer would have to demand it, and they would only likely do so only if they wanted to WiFi certify their Roku TV).
Finally, WPA3 isnt very secure (re: Dragonblood et al) and is still a WIP (Work-in-Progress), which is another reason there is no great rush to include support for it:
https://www.snbforums.com/threads/are-all-the-known-wpa3-security-flaws-fixed-now.73290/
Not sure what you mean by "compliant with WiFi standards" - clearly Roku devices are "WiFi compatible" - but Roku devices arent WiFi Certified, nor will they ever likely be (same for their competitors).
I dont know/know of a single person/consumer (you even bought the Roku TV not knowing/caring enough beforehand) refusing to buy a wireless networking device because it "doesnt have WPA3" support. I'm not suggesting they dont exist, just stating that they have no meaningful market impact.
Again, Roku will likely include WPA3 (and IPv6) support (probably at the same time) at some point in the future, once the WPA3 standard has settled more and SoC support solidifies (which both their and Roku TV manufacturers' hardware products can take advantage of), but that wont happen until this fall at the earliest (with the release of OS10.1/11 and new models), and likely not until fall 2022.
