We have released the latest AcuPOS powered by IIG for 2021R1 and 2021R1 IIGPOS User Guide.
The latest AcuPOS by IIG build is 105 and User Guide works with the latest Acumatica ERP 2021 R1 build 116.
This information can be found Community >Product Downloads > Add-ons and Integrations > Acumatica Point of Sale (POS) powered by IIG