ArcGIS Pro Can not edit model exported from the external toolbox

[LilUzi]

Hello everyone. I am a college student studying GIS and this is the first time I ask a question here.

My ArcGIS Pro version is 2.9.0 and I have just saved my toolbox  (10.5/10.6 toolbox) which contains the main model and a sub-model in Model Builder.

Later, I open a new project on my laboratory computer. I input the toolbox mentioned before. Once I open the main model and sub-model in ArcGIS Pro I can not see anything on the screen and I could not edit anything. I have attached a figure for reference. Could you please help me to figure this out.🙏

My English is not good and hopes that you could understand. Thank you for your attention and look forward to hearing from you.

[RichardHowe]

I'm not sure why you're saving it as a 10.5/10.6 toolbox if you created it in Pro and you're also opening it on the lab computer on Pro. That "save as" option is to make it usable on older versions of ArcMap, not ArcGIS Pro. You should just be able to copy it from your project folder in windows explorer for use in Pro without the need for a "save as"