If the cracks are not to wide, a colored putty would work better than wood filler. You can mix a couple colors together to match the stain.https://www.acehardware.com/departments/paint-and-supplies/patch-and-repair/wood-filler/10777?x429=true&utm_source=google&utm_medium=cpc&gclid=EAIaIQobChMIvqSBkbqN3gIVCQ9pCh0acQFTEAQYAyABEgIxUvD_BwE
Jeff has the answer as usual then u can varnish over it if
I’d get the color match putty sticks from reliable in Elk Grove Illinois bought out by JCLicht and ask for cat it’s free
Gary