You can display only .blend file by enabling Filter (icon in header), but your setup of Filter is not remembered when dialog window is open again (even when Saved as Startup File ... to be precise - it can be saved into Startup file while dialog window is opened whe saving as Startup File, but it bring this window open anytime you open Blender (that is not wanted) and even more this window is missing Cancel / Open buttons ... so totaly useless.
As workaround you can ...
Add a Workspace, name it "Open" (or what ever) and switch View3D editor to File browser editor.
Set Filters as wanted.
Switch back to default Layout workspace and go to File > Defaults > Save Startup File
For opening file click on Open workspace, drag&drop file to anywhere out of File Browser editor and choose Open command.
What looks like a bug here is the ignorance of saving the workspace changes made by user. I had to save file as regular .blend and switch this file with existing one called startup.blend.
Directory of this file depends on OS, for Mac it is
Than it works like that ...
Right ... that is too much scratching :) Would be part of defaults.