The excellent Spatial-Gardener Addon for Godot needs it’s assets to be .res files and one way to do that from Blender (or probably any 3D-object) in Godot is:
The object should probably a single mesh (ctrl-j in Blender), export it as a .obj (probably optional but easy to just export the single mesh that way).
Select file in Godot’s file browser, in the „Import“ options tab (up left a tab next to the Scene tree view), change „Import As“ to „Scene“ and press the „Advanced …“ button.
Press „Actions …“ on the upper left and choose „Select Mesh Save Paths“, select a folder where you want to save the mesh and press „Reimport“
Voila!