Lgb part 10260 insulates. It replaces joiner 10001. See the tab on the metal joiner, so it resists coming off the rail.
There are also insulator track pieces pre fab that have been made over the years, some looked like a grade crossing, some were accessories to signals and are just a short track with a gapped piece of rail. There are mainy examples of those, 1015u, 10152, 10153 etc
Mind you the 4 digit catalog numbers are now getting 40 years old, so unless you like the style buy a 5 digit catalog number.
Personally I would go with a track piece instead of the plastic joiners