It seems that you are experiencing difficulties opening a PSDT file in Affinity Photo. Here are some suggestions to help you resolve this issue:
File Format Compatibility: Affinity Photo may not support the PSDT file format. The PSDT format is not a standard Photoshop file format and may not be compatible with other image editing software. It is recommended to save the file in a standard PSD format instead.
Saving as PSD: When saving the file in Photoshop as a PSD, make sure to select the correct file format. It should be saved as a regular PSD file, not a PSD image file. Double-check the file format options when saving to ensure it is saved correctly.
Smart Object Conversion: Affinity Photo may handle smart objects differently compared to Photoshop. When opening a PSD file in Affinity Photo, the smart object may be converted to an embedded layer, which can affect its functionality. Try converting the smart object to a regular layer in Photoshop before saving and opening it in Affinity Photo.
Layer Mask: If the smart object in Affinity Photo does not have a mask, it may be due to differences in how masks are handled between the two software. You can try recreating the mask in Affinity Photo manually to achieve the desired effect.
Compatibility Issues: It is possible that certain features or functionalities of the PSD file may not be fully supported in Affinity Photo. This can result in differences in how the file is displayed or edited. In such cases, it may be necessary to make adjustments or find alternative methods to achieve the desired outcome in Affinity Photo.