It’s affecting the UI and sprites. (If someone can link how to make the UI high quality, that would be helpful.)
Are my sprites too low resolution? Many of them are natively 250x250 in size - but that’s because they are supposed to be small and take up a fraction of the screen (and because I am worried about performance). Should I just make the source images larger (like 800x800) and then resize them in the scene?
You mentioned 250x250. A lot of low-end hardware struggles to resample when image data isn’t a power of two. The closest is 256x256. Maybe that’s what you meant. If not, and if it’s not the Quality Settings which @DevDunk mentioned, it’s worth a look.