Arlo Pro 3 Cameras, GoControl Sensors, Nest Smoke/Co2 Detectors

I can’t speak for all the items you list but here is what I believe is the current situation for the others. I have only used the Classic app so the Nest situation in particular relates to that.

There is official support for at least some Arlo cameras models, it could be the Arlo Pro 3 being so new is not yet added. As you have already purchased everything involved you should try it.

For Nest the situation is both more complicated and worse. There is no official support for Nest, there is however a free 3rd party integration. Unfortunately as you may have heard Google announced they were going to shutdown the former ‘Works with Nest’ feature which is/was being used to link them to Smartthings. I do have a Nest Thermostat and Nest Protect connected via and still working using this 3rd party integration but if you have not already enabled this it may be too late - especially if you have allowed your Nest account to be ‘migrated’ to a Google account. Google do intent to provide a replacement mechanism but it will have a lot more software restrictions and there is as yet no way to know if it will then be possible for someone to develop a new method.

Interestingly, there have been some comments saying that if you have Home Assistant running you can still link Nest products to that via a different approach. Once that has been achieved you can then use MQTT on both Home Assistant and Smartthings to ‘share’ the Nest from Home Assistant to Smartthings. I have not tried this myself and clearly this will be a lot more work but this might provide a solution. It could be that this approach might also have more chance of working in the new Smartthings app because they then would use generic thermostat and smoke drivers - obviously with the likely loss of some features.

With regards to the current/former Smartthings solutions see the following.