Migrate multiselect taxonomy values from node with csv
I found it myself.
This is working for me:

process:
  title: title
  body: body
  field_company:
    -
      plugin: explode
      source: categories
      limit: 100
      delimiter: ;
    -
      plugin: entity_generate
      ignore_case: true
  type:
    plugin: default_value
    default_value: company


and a CSV like this:

id,title,body,categories
6,company,body text,"cat1, some text;cat1, some other text"