I don't know these apps and I'm not sure I understand your problem. But if they use tabs, then shortcuts should also exist to navigate. You can change these shortcuts as you like. If the tabs are only accessible through a menu, you can try the "Select or Show a Menu Item" action. If that doesn't work either, there is the possibility to click relative to the window or to search for specific text or images.
There is nothing in either app at the menu level that allows you to chose the next or previous tabs, or cycle through open tabs.
Affinity has tabs, but Command+` allows you to flip between them, so in effect it treats tabs as windows. I guess I can reassign that shortcut, but I'm not sure how to go back and forward with Command+Option+ left or right arrows.
Basically, I'm trying to bring into Affinity and Tradingview the same workflow I have in Chrome.
More important to me is Tradingview, which overtly works on the basis of tabs and windows, but again, nothing in any menu to allow you to cycle between tabs, but the app is basically forked from a browser-based interface, so I think it should work much like Chrome does.
You can see in the attached screenshot the tabs at the top of this window.
I want to be able to go back and forward between them using Command+Option+ left or right arrow.
Obviously I can mouse click, but I want to be able to stay on the keyboard.