This is a workaround using Reclassify by layer tool (so it is not a direct answer to your query).
(1) Prepare a classification table by a spreadsheet software ( I used MS-Excel).
(2) Drag and Drop the Excel file to the QGIS then it will appear on the TOC (Layers Panel).
(3) Start Reclassify by layer tool and select Min, Max and Output fields from the ...
I have created a model you can download here from my github repo.
Thats how it looks:
r is the input raster
NClasses is a numerical input greater 0 (the amount of classes you wish to have)
you need to set a dependency for "Reclassy by table", because "Raster layer statistics" needs to execute first
you need to insert a ...