Are there any apps that focus exclusively on improving vocabulary?

Hi everyone! I consider myself somewhere between A2 and B1 with Dutch and can understand most things, but I noticed that one of my biggest issues right now is just not knowing enough words.

I was wondering if there are any apps that teach words exclusively and let you practice, like flash cards?

I've only used Duolingo so far and I think the app lacks a lot in that sense. I would appreciate any input.

Thanks in advance!