@iDavid-956 

On an A20, and Tether is on my iPhone 12.

Same set of icon's you stated.

Roku came up as 3 "."s as I got it recently and this is the first time I looked.

Selected the icon on the page for the Roku, used the 'Computer' (looks more like a Monitor), and it saved.

I did leave the name as what it defaulted too,"RokuStreamingStick" though. Changed the name to "Roku" and the icon selected stayed. Never changed to 'TV'?

I've got V3.4.36 (Build 43) of Tether.

@IrvSp Glad to know I'm not alone. 
 

The TV with "TV" written in the middle is the correct icon I had before for the Roku's in my house since there really wasn't a better icon for streaming devices. They essentially turn your TV into a smart TV so I figured that's good enough. 
 

Unfortunately, the smart TV icon will only auto appear if I type the word "Roku" somewhere in the description but then it won't save the icon when I press save. The other option is to do it manually but that smart TV icon isn't available to choose from. 
 

So if the Tether app would only save the icon when it auto detects it, the problem would but solved but it doesn't. Manually selecting it then would solve the problem but not all the icons are available to choose from. So if tp-link were to fix either problem, I'd be happy. 

@iDavid-956 

I never got the 'TV' to appear, no matter what I did?

Maybe it is because Tether actually 'knew' what I had, or the router did? It picked it up as "RokuStreamingStick+" which it is. Maybe you have a different model? Even though I changed the name, the icon didn't?

By the way, I have MANY devices with the 3 dots. Also a FireTV Stick has that. So does my Smart TV. There is no TV on mine at all, only the base 8 choices you see. Also, others are basically 'unknown'. Our Amazon Echo's and my Apple Watch as well as some IOT's, all have 3 dots. I don't really look at the icon as much as the names with can be edited (like naming the iPad's and Phones so we know the user of them) and are correct.

@IrvSp I think this auto detection is a new feature for certain new tp-link routers. On my Archer C8, I had to label all the devices but there were way more options to choose from that are missing on this Archer AX21. The only device that didn't have a corresponding icon was my brother's  Apple Watch. I would choose the generic icon for that. 
 

We briefly tried an Eero mesh router. It ended up not being what we needed so we switched back to our Archer C8 but I noticed they had a lot more icons to label devices. I'd hoped that tp-link would have updated their app to have more label icons for different devices like the Eero had. 

@iDavid-956 

Interesting!

That info sort of points to the ROUTER and the holder of the icons, not Tether?

Doesn't matter to me, the NAME is what is important, especially on a LAN where duplicated device types exist.

OP did state changing the name to "Roku" the TV icon appeared but it wouldn't be saved? I tried that on my Roku but never saw the TV icon? Could be a problem between Tether then, not honoring the Router's icons?