After the Galaxy S21 and S21 Ultra teardown videos, the third phone of the family received the same treatment – here is the Galaxy S21+ disassembled. In the process of taking the phone apart, YouTuber PBKreivews discovered the distinction between single and dual-SIM models.
It’s mostly in the software – all S21 models have two SIM readers, but in single-SIM versions one of them is disabled. It may be possible to flash a different firmware to enable the second reader. You’ll also need a new SIM tray, one that can hold two SIMs.
The Galaxy S21+ in the video is the Exynos-powered version and it lacks mmWave antennas, meaning it only supports sub-6 5G. You can watch the S21 teardown to see a unit with mmWave antennas.
A harder fix would be a failed button on the side – the flex cables for those are sandwiched between the screen and the phone’s frame, so you have to remove the screen to axes them. Also, (as with other Galaxys) the battery is glued in without pull tabs, making it harder to extract.