SceneryDesign.org 
It’s time for an early Christmas gift this year, I have just released a new stable release of ModelConverterX. In version 1.8 all the changes that have been made in the last year are included and if you have tested the development release you will have seen them already. There have been over 100 changes compared to version 1.7, so I am not going to list them all here. But the main new features are:
- ModelConverterX using .NET 8.0 now, instead of the .NET Framework 4.8 as the previous versions did. So make sure you have the x64 runtimes files for .NET 8.0 installed.
- A new options dialogue has been implemented. Settings that are related to the import or export of objects have been moved to the import and export dialogues. The remaining general options are shown in a new, more user friendly form.
- MSFS 2024 MDL objects can be read, as well as the KTX texture format that MSFS 2024 uses.
- The performance of the LOD Creator has been improved a lot, especially with big and complex objects. And the MSFS 2024 specific LOD structure is supported better.
- glTF objects using the meshopt compression can be read.
- It is possible to place and move attached effects and lights interactively in the 3D preview now.
- A Building Creator Wizard has been added that you can use to quickly generated buildings from a footprint.
- And many, many more (small) changes.
So enjoy this new release. The development release will be updated to version 1.9 now and I have already started coding some new features. So these will appear soon in the development release.
I have followed both the manual and responses to other users having the same issue. I have ensured I have a .net framework version later than 4.7.2 and the latest release of the Visual C++ runtime files, and I cleared the SceneryDesign.org folder in my AppData folder. The app still does not open, a blank tab will show for a split second then disappear and nothing will happen afterward.
Do you have the .NET 8.0 x64 desktop runtime files installed as mentioned in the manual? Version 1.8 and later use .NET 8.0, while prior version used .NET Framework 4.8.