From my very limited experience, the best way to do “Hole filling” is to use Meshmixer (free-of-charge software at 2023Jan). Especially, the sculpture tool.

Visually, it is perfectly. But, as a computation analysis I will need do more analysis on those tiny changes, stay tune.

Here is a detailed comparison of the process, you can find my post on it.

My first attempt after obtained the mesh from POP2 was document here: 3D mesh issues after scanning - Dao

Then, there are some issues I observed: Fix 3D mesh issue with Blender - Dao

I tried hard initally in Blender: Fill big hole in Blender is not easy - Dao

But I accidently found Meshmixer works: Fix big hole in 3d mesh - Dao

Here is the final mesh: So I have my fist on computer, what’s next? - Dao. It is way much smooth. What’s more good about it is that I run my first computational fluid dynamic simulation without any error. That’s how crazy it was.