Laptops are a special problem for burn-in (well, desktop computer screens are even worse since you are less likely to hide things), because of components that stay in the same place (the Mac menubar, the Dock if you don't have it auto-hiding) and screens that stay on for hours.
TVs rarely have a component that stays in the same place, although those that are always tuned to the same sport (score boxes) or news channel (chyrons (the technical name for those text banners and logos) at the bottom of the screen) are exceptions, and phones, watches, etc. don't stay on for hours of constant use. Even LCDs will burn in in special cases - look at an airport arrival monitor!
Widely circulated OLED laptops are too new to know how big a problem burn-in will be - but "it works for TVs and phones" doesn't necessarily mean it'll work for laptops. The sample size of early OLED Thinkpads and such that are getting to be a few years old is tiny, because OLED carried a $1000+ price premium. The more common OLED laptops with their premiums of a few hundred dollars are too new to be expected to show burn-in yet.
The "no new CPU until 2021" isn't (technically) correct. There will be a new 45w CPU before then (could be any time from now until May or so) - but it'll be YetAnother Lake 14nm++++++++. That's Comet Lake, if I have the names right. There may even be StillAnother Lake 14nm++++++++++ stuffed in there in early 2021 (Rocket Lake), before a 10nm CPU in late 2021 or early 2022. The mobile CPU roadmap leaks I've seen only go through 2020, and they clearly show Comet Lake as the 45w CPU through then.
Rocket Lake shows up on desktop roadmaps that stretch into 2022, and it doesn't get replaced by a 10nm CPU until the end of 2021 or even early 2022. Since the H-series chips are kind of intermediate between the mainstream mobile parts (which mostly transition to 10nm over the next year) and desktop parts (which are stuck at 14nm for a long time) their fate is not clear.