Plus stands for 'more of it', and the S21+ has a bigger display - at 6.7 inches in diagonal, it's a lot closer to the Ultra's 6.8 inches than it is to the S21 proper's 6.2. Beyond the size, however, it's more vanilla than it is Ultra - the resolution is 1080p, and the Adaptive refresh rate handling is the half-there variety, but Adaptive it is nonetheless.
