I have an SE which I'm holding on to this fall when the 13 Mini comes out or when Apple decides to put 12 Mini on sale with a Gift card which they do during the Black Friday event. The SE feels slow now and the bloated OS 14 plus the apps made my meagre 16Gb SE pretty much useless to hold the apps I used to be able to do. But I only do lite social media stuff. Initially I thought about the SE 2020 but then I decided I want to own a premium iPhone in the class of an iPhone 12. I never had a premium phone and the more I try the 12 Mini, the more I really like its features. I plan to use it with Air Tags mainly for its precision finding with its U1 chip that only the iPhone 11 and up supports. Once the borders are open and COVID is behind us, the 12 Mini would fit me better. So I'm on a fence right now.
By the way, the screen size of the SE 2020 isn't as small as you think compared to the 12 Mini and you really need to like the PWM of the 12 Mini if it gives you a headache or not. I had to try the 12 Mini's screen for a long time to make sure that the PWM on the Mini isn't giving me a headache. Certainly, the SE 2020 screen color and whites are somewhat better, in my opinion and how my eyes see them, compared to the 12 Mini.
PWM stands for Pulse Width Modulation is a method the 12 Mini uses to display the screen and is subject to flickering. I did notice it more compared to the SE 2020, but not enough to cause me migraine headaches. Your experience may differ. Best to try out a PWM and play with it for 15-30 mins and if it gives you headaches, then you know PWM is not for you.