Obligatory: You can buy a cheapo $50 DisplayLink USB adapter to run a second monitor up to 1080p[1]. I have a really old Monoprice USB 2.0 adapter I still use that even has my security camera video feeds on. Does totally fine.

1. They have USB 3.0 ones that do 1440p, but I've tried a lot of them and haven't found one with good performance on Mac.