I feel like I lack basic general knowledge

Watching daytime television has been helpful for me. Quiz shows too. Travelled a lot as a child, helped geography.

Curiosity

I have always found that doing general knowledge crosswords helps and watching quiz shows where general knowledge is tested. If it isn’t fun I doubt you will be very successful at retaining the information.

Reading, reading and more reading. Reading newspapers, novels, magazine articles, internet blogs, even Facebook pages (but use a good pinch of salt and a large helping of common sense on the FB pages, they may be "fake news".) Talking about things to other people and listening to what they have to say. Being interested in what is happening, in other people's stories and lives, their work and their holiday destinations, in how and where things are made,

I am not sure that you can learn "general knowledge" by rote, it is more something you pick up as you live life. You may forget a lot of what you read or hear, but more will stick than will be lost - and you probably know much more than you think you do.