For those who are trying the latest Blender2MSFS2 from GitHub, I have the batch LOD export working it seems. It really needs more testing, and mikea.at has made it available for just that.
I have been able to create 3 LODs, batch export them, and have them function perfectly in the sim. I expect problems elsewhere, but I'm still working on that.
If you want to try the batch export, here's a suggested workflow: (This assumes that you know how to use the Outliner and create collections.)
Work Flow:
1. Develop LOD models in labeled collections (x00, x01, ...)
2. Select all, but make sure nothing else, like image plane guides, cameras, suns, etc. are selected. (I keep another collection for just such junk.)
3. Open Export dialog and set up as you would a new export (..\texture\, copyright, save settings). Check Batch Export, Generate/Append XML, give it a name and generate a GUID.
4. Include Selected Objects and Custom Properties. The others appeared in mikea.at's latest version. I don't know what to do with them yet.
5. In the Geometry section, I check Apply Modifiers, since I always work parametrically. If you've already applied your modifiers, leave it unchecked.
6. Export to your chosen directory.
7. (Important) Next time you export these models, UNcheck Generate/Append XML. If you don't, you'll have the LOD minsize xml values reset to 8 and 4 instead of what you set it to as you placed and edited the model. Also, make sure the name you use for export does not have the LOD level concatenated; the Batch exporter will take care of that.
You can now leave Batch checked for subsequent edits. This way you can work on several levels and only have to export once for each test iteration.
As an additional helper, Here's how to figure out what minsize value to edit into the exported .xml file:
"I've been using LODs for quite a while now, and the mystery of the meaning of the "minsize" puzzled me until I 1) read that the sim computes a sphere around your model and measures the sphere's size in some unit value, and 2) you can view the value by selecting Options-Debug LODs-Display External Models LOD from the Dev menu bar. Now, with your model selected (white rectangular volume) you can zoom in and out and note the value in the overlaid display. You will now see something like: ‘LOD[0,1] Size[73.45]’. The first numbers in brackets are the current LOD (numbered from 0), a comma and then another integer showing the number of LODs available for this model. If you have only one LOD, it will show a 1. The LOD is like a fence between showing one model and the next model. The minsize, therefore, does not necessarily depend on distance; rather, I think it depends on the "enclosing volume". Since I make long, narrow bridges, I end up using large numbers for the first minsize. Smaller, more compact structures will require a different set of values for the same distance. I'm certain this is probably the case with P3D also. You turn off the LOD value viewer by going to the same menu and unchecking that line."
The latest SDK update has expanded the LOD "analysis" facility quit a bit. I think you can figure out how to use it, now that you know it's there. Also, perusing the code, the sequence of minsizes starts at 4 an doubles backwards; e.g. Your .xml exported file will show an initial minsize value of, say, 32. The next will be 16. The next will be 8, and the last will be 4. Edit the .xml file as needed to make your model behave in a "platform-friendly" manner.
Fair Warning!: I had perfect results for original files/models. I ran into a problem with textures on an older model (pre-2021-8-5).
HTH