How to use WP-CLI / WC-CLI to bulk import 1000s of products (variable and simple)?

I am a junior developer and I have been asked to work on a wordpress site that has previously been using All Import plugin to upload products. The problem is, this is not functioning properly, and is very slow. (often throws an error 524).
My question is, where do I start with writing the script needed to use wp-cli to import products instead? do I need to write it as a plugin? or just use the wp-cli commands. I have wp-cli installed locally on a windows machine, and it is working.
i have been researching this for a week now and i can’t find any definitive direction with it.

any help would be appreciated.