were that many people using 3D-plastic printing, back in 2019

3D printing was already pretty common in 2019. I had a small hobby printer by then.

But I’m not entirely convinced that the above tray is 3D printed. I can’t see any obvious artifacts such as layer lines or the tool path of the top layer. It is quite a large object, and would likely need to be printed in multiple parts, or on a specialized printer. Additionally, untreated 3D prints are generally not recommended for items which will repeatedly contact food, as the rough surface is difficult to fully clean.