The definition we learn for the 器 kanji is “container”, but I think it would be better for us to learn it as “tool” or “instrument” (with container maybe as a secondary definition, if at all). With the exception of the vocab word 「器」 itself, pretty much all the vocab we learn uses it more in the sense of a tool. The meanings of all of these are immediately obvious if you think of it as tool/instrument.
器用 - dexterous - good at using tools
楽器 - musical instrument
食器 - eating utensils - food tools
兵器 - arms/weapons - soldier tools
電子機器 - electronic equipment - electron machine tools
加湿器 - humidifier - add damp tool
Pretty much all the way down the list the meaning “tool” fits much better than “container”.
And there are plenty of kanji that we learn where the meaning we were taught for the kanji differs from the meaning of the vocab containing only the kanji. I can’t think of all of them off the top of my head, but 約 comes to mind.