Are you sure about the AMSI thing? BD free uses the same engine as the paid version so this is not expected. Can you tell me the method you used to check AMSI?
Edit: Looks like you're right. Apparently they had AMSI before but not anymore. WTH!!! I need to test if this is still true. This applies to even paid Bitdefender products.
This feature was in the 2019 version of BDIS, it was enabled in the main interface settings under the General tab.
community.bitdefender.com
Edit2: Well, things got interesting. Bitdefender paid versions have AMSI protection, but it's not enabled by default. Really weird. So yeah I guess BD free version don't have AMSI as there's no way to configure it to enable the feature.