I searched far and wide for a replacement plate or a 3D model of this Ridgid 12" sliding miter saw throat plate insert, to no avail.  The model was discontinued and is unavailable anywhere.  The old plates became brittle and broke apart; this is much more solid and stronger than the original.  I suggest printing in PETG or an even stronger material as PLA may be prone to shattering during a kickback, for example.

This throat plate insert fully occupies the recess in the saw table to avoid build-up of sawdust around its edges.  The saw requires two identical plates.  The throat plate is 19.25in long (489mm), designed in inches.

Print the model in one piece if your print bed is large enough for it (489mm).  But because my 256mm print beds are too small, I split it into two parts using Bambu Studio's Cut function with Add Connectors using 4mm/4mm plugs.  You can do likewise.  Cut near the middle, both parts will just barely fit on the MK4/X1C beds provided you have no brim.  Glue is optional to join them permanently, but I don't see the need.

It took about 2.5 hours to print with these settings:

Printer: MK4 using input shaper
Nozzle: 0.6mm Prusa ObsXidian
Filament: Prusament PETG
Slicer: Used default Prusasclicer settings for MK4-IS w/Prusament PETG (240/90 0.32mm), while increasing top/bottom perimeters to 6/5 and infill to 40% for strength.
Supports: No support is needed when printing with the screw slots facing up as in the included STL.

The picture with the two-piece plates installed shows a missing screw (dropped and lost in the grass during installation) but they still worked well.