And quarter round won’t work?

Mine has a quarter round all around the edges of the hearth.

I think like g&s- I would caulk that seam. I would use grout caulk in a tone that matches your mortar (maintains the straight line at the wood). You can get sanded grout caulk at a box store or good tile store.

So minor, I wouldn't touch it. You're the only one that will see it.

If it's just for housekeeping, I don't see why caulk doesn't work. You may have made a "chamfer" bead sitting on top the wood, which is why it peeled off. I would fill the gap and not have the caulk extend above the wood surface. Dark colorized caulk (not painted), so it looks just like it does now, which is preferable IMO to a "scribed" look of flooring.

Agree with Hallett on this one. Find a sanded caulk that matches the grout on the brick.

Thank you everyone! I guess I used the wrong type of caulk since it was for painting over and more for wood trim etc. I’ll try the sanded caulk that some of you recommended.

It is a change on plane and or between different materials so it needs to be a silicone caulk as well.