It is mandatory to register.

If a store sells goods (including goods and related waste materials, such as packaging) to Germany through AliExpress that are subject to EPR regulations, and fails to provide AliExpress with valid unique identification codes corresponding to these EPR product categories before the compliance period, or fails to pass the review due to inaccurate information submitted by the store, AliExpress will have a legal obligation to stop selling your non-compliant goods in the product categories to which extended producer responsibility applies.