No, you sign up with Tuya, you select the device you want by functionality, the logo on the box and manuals, and Tuya manufactures it and delivers the final product to you, ready to sell, with their software bundled. They are the manufacturer. You are their customer.
Example: You want to make lots of money. You want to sell a light dimmer, using the latest Matter/Thread technology that seems to be flavor of the month. You want to sell it to Scandinavian customers.
You could develop your own hardware, using chipsets that support the Thread protocol. You could then join the Matter consortium and have your device certified. You may also need certification for European RF emission standards.
Then you have to design the software, first the firmware, and also the user interface.
Then you have to write your own manual, possibly in a few languages and checked by a native speaker as users hate the equivalent of Chinglish.
You need your own barcode and QR code on the packaging so the cash registers can sell it. Another consortium to join.
What will your device look like? Smooth flowing shape, but able to fit two side by side on your power point? White, cream, or a distinctive color? Do you expand your range for stockists to have a few of each? What if nobody buys your pretty Russian blue one, just for political reasons?
You have your picture on the package, the NEW Sven Matter dimmer.
You manufacture a thousand from the cheapest Chinese manufacturer you can find, and discover there is a flaw and you need to do a product recall, or your technical support number is overwhelmed. Oh no!
The other option: You sign up as a Tuya customer. You tick the box for Matter. You tick the box for Dimmer. You tick the box for white as there is no other choice available for orders of less than 100,000 units. You supply your photo to go on the packaging. You tick the box next to the language you want the manual and user interface to come with. You order a thousand units, pay for them, and they will be delivered to the nominated address in a few weeks. Want a sample - no problems. Need more? Just reorder.
They come with all the appropriate certifications and approvals already done. The users sign up to the Tuya cloud, using an app (the 721’st one you are still discovering) that has your smiling face beaming at them, and the device data is then transmitted, via the Tuya cloud to automagically make their device work. If Tuya have any firmware updates, they push them via their own inbuilt infrastructure.
Want to expand to other countries? Go back, tick the extra language boxes and your manuals will come with multilingual sections, and the printing on the box will be in the language you specify. FCC certification? Tick the box and the symbol will be included on your packaging. Easy.
You heavily promote your new product, safe in the knowledge that the product you are selling has the backing of a recognised manufacturer, purchasers noticing your product is Matter, and also Tuya, Amazon, Apple, and Google compatible.
You are busy counting your profits…
Easy choice?
Go check out the Tuya website. They are an OEM. That is their selling point - a cookie cutter solution. What they put inside their product doesn’t matter to you as their customer, even though it does for HomeAssistant users who are your customer, and they are attempting to integrate their new Sven purchase into their HomeAssistant system with varying degrees of success. They curse the Sven app they downloaded from the QR Code on the box, and madly apply all firmware updates it offers. You remain blissfully unaware as you are busily counting your new found wealth.
You re-order another 10,000 units. Unbeknown to you, Tuya have a new SOC module that has the same functionality but from a different chip manufacturer, that costs them a few cents less in lots of ten million chips. This is the one that gets incorporated into your next manufacturing batch. The users that use the Sven software receive a new update and everything seems fine. The HomeAssistant forums light up as they discover their custom firmware they developed for the old SOC doesn’t work with the new Tuya modules. They busily start reverse engineering to integrate into their existing system. Rinse and repeat!
Going back to your original post, you don’t need to continue to find 720 more instances of the rebranded Tuya app once you realise what is happening behind the scenes.