PSD MockUp File - can't open PSB files now with Photoshop 2021

where is the solution guys? 

Not all smart objects are PSB files.  If you used Replace Content on a Mockup templates smart object layer and saved the mockup PSD or PSDT the smart object layer's object may no longer be a PSB file.  It could be an ACR RAW file, an illustrator Vector File, a  Photoshop image file like a PSD, Jpeg, Png, Tif etc.   Not all Mockup templates contain smart object layers that only contain PSB object.   When you convert Photoshop layers to a smart object layer the object will be a PSB object.  If you place in as image file the layer's smart  object can be a RAW file, a Vectot File  or a Photoshop image file like a PSD, Jpeg, TIF etc  I find Mockup templates that have  Smart object that a RAW, Vector, Png and jpeg can be  a problem.  I recommend  creating Mockup templates that do not have object that are those types object. Opening a RAw Object will open in ACR,  Opening a Vector object will open in Illustrator,  While openind a PNG and Jpeg Object will open in Photoshop. Place may have trimmed a png file transparent boarders, and with a Jpeg object if you add layer editing the opject you nust flatten the layers so save will work to have photoshop the update the smart object laye's object