Acme Tools - Sawdust mixed with wood glue makes a great “putty” to fill in small holes and voids in wood. You can keep various types of sawdust handy to match the
DIY Wood Filler - 3 Ways! - Pine and Poplar
Make Wood Filler With Sawdust – How And Why? | Woodwork Junkie
Is this gap too large for wood glue/sawdust to fill in? : r/woodworking