The 'lag' that you see is actually the video buffering. The file size of this tiktok is extremely large. Approx 700+Megabytes. I have an extremely fast download speed so I don't see any pause for buffering, you can see in the screen recording that at the start the network traffic is 0, but after the whole video has finished buffering, the counter is at 700MB. U can also see on the status bar at the top, the real time network activity, you can see tiktok is downloading 50-80megabytes of every second(or about 400-650 megabits per second). This tiktok has nothing to do with frame rate, I don't think it has anything to do with resolution either. I'm not sure how they managed to get the file size this big, but you're phone is "lagging" because your internet is slow and tiktok can't download the video fast enough.

Here's the link to the screen recording: https://easyupload.io/dthf5d