You can onboard a compatible TV with the new SmartThings app by signing into your TV with the Samsung account you use in the new SmartThings app, a factory reset may be necessary if you were signed into the TV previously.
If you use the same Samsung account to log into the SmartThings classic app, you should also see and be able to control, except for turning on, the TV from SmartThings classic. However, longstanding SmartThings users will may see that the TV is on a different location than their Hub/devices. Additionally, because account migration isn’t fully rolled out that may cause a separation between the account where your Hub/devices are vs the location where the TV is added.
This isn’t a new update but there is continued work on the ability to turn a compatible TV on with both of the SmartThings apps and the ability to move the TV device between locations.