In Odoo 18 I succeeded by importing on two steps:
1. Import BOM definition without Components and Operations
2. Importing BOM Components as second import. I was importing only:
--> BOM [External ID]
--> add column with [Product Variant External ID] and map it to [BOM Lines / Components / External ID]
--> [BOM Lines / Quantity]
--> [BOM Lines / Product Unit of Measure]

I hope this helps!

Thanks for response!

I know how to create in form view and also how to create with import using IDs, but I don't manage to import with plain text. As long as the components have no variants, everything is fine, but since there are variants, I face this problem...

imho didnt understand correct issue, can i know how you are importing the data to the system ? using the default odoo import export option right ?

Yes, exactly. But I can call the column "product_tmpl_id" and import "T-Shirt" or I call it "product_tmpl_id/id" and import the related id (like "__export__.product_template_51_46199f68").

Here you are specifying the product.template only, use the field product_id in your file and specify the variant in it. You can do one thing, create a BOM with specifying the product variant field and export the records with the fields product.template and product.product .

But see, for the component I have both, bom_line_ids/product_id and bom_line_ids/product_tmpl_id.

Yes, there will be both, so what is wrong