I have the same problem on Delphi ver. 10.3 importing a Net 5.0 assembly.
I figured out that if i have fewer than around 7 property/functions the import goes well.
If i have more then i get the 80131124 error when adding the assembly.
Delphi is perfektly cabable to call more than 7 functions. It is just the IDE that can't autogenerete the interface/TLB .pas file