Were there blinds on the window? If so, open them.

What is the relative humidity set at and what are the outside temps? Bathroom windows will be subjected to already higher humidity levels so you need to be careful here.

Is there proper venting in the bathroom? Is the fan on a timer?

Is that photo oriented wrong? It doesn't look like a window sill to me, but maybe I'm just looking at it with my eyes inverted. Probably just need another cuppa.

As I've written here before, it makes absolutely no sense to me to install a humidifier, and then use a fan to send all that nice humid air from showers outdoors, along with some of your house's humidified air. For goodness sake, just open the bathroom door after your showers. Better yet, if you're not too modest or live alone, shower with the bathroom door open.

Like David, I can't quite make sense of the picture. Is it upside down? Is the water stain on the trim around the window? I'm not seeing a window sill either.

Sorry it was inverted definitely the ledge Of the sill

Step back a couple of steps and take another pix.

Because it looks like to me that condensation has rolled off a piece of quarter round and seeped behind the window casing in a gap that shouldn't be there.

The logic behind not wanting uncontrolled humidity into your home is the same as not wanting uncontrolled air leakage. Both are necessary and need to be moderated to maintain indoor air quality, maximize energy efficiency (not as much on the humidity aspect), and have a comfortable environment for inhabitants and building materials.

If the only condensation problem that you are seeing is in the master bath, then the humidifier isn't likely the issue (although that will certainly come into play in frigid temps and more condensation throughout the home). Run your bath fan more to pull that moisture out. Make sure that the blinds/window treatments are open for circulation when privacy is not needed. If the problem is located in a specific area, the solution is most often found there as well.

As for the home as a whole, once again, this is something that you will want to monitor depending on how cold it gets where you live. Colder temps require lower RH in the home to avoid condensation, although sometimes you may just want to accept it and wipe off the wet surfaces when talking subzero temps. 20% RH is not comfortable for most people.

Here’s a better photo how do I repair this?

Replace the sill w/ an acrylic solid surface material (Corian, etc.) (Wouldn't hurt to replace the side jams, too. You could use less expensive PVC on the side jams.)

Home Depot sells one called 'Siltech'. Available in different sizes. Standard woodworking tools are all that is req'd.

Siltech

Turn on the bathroom exhaust fan before you turn on the water. Run the fan for 30 minutes after you leave the bathroom & leave the door open, esp. after showering. Or get a fan w/ a humidstat built in. Wipe up any condensation after you shower. Also, a storm window might help.

When you replace the sill, I would check to see how well the window opening was sealed. You might end up wanting to pull all of the window casing and using a window & door low expansion canned foam to seal the window installation...IF this detail was neglected when the window was installed. And maybe add a storm window...

In your second photo, is the paint blistering, or is that water pooled on the sill? Either way, I'd probably just sand the sill and repaint it. But then I have an older house.

Adding a storm window sounds like a good idea.

I would sand and prime (good quality primer) and repaint too. I can see by looking at your window, you have way too much humidity. What kind of shades or blinds do you have in there. That type of moisture can be on the windows, when you have blinds that shut tightly. I would also add a white storm window on there. If you get humidity like this on all your windows, there is definitely something wrong, with the humidity in your house. Also, until you can get it resolved, have towels, or cloths, very close to it, to wipe the window, and leave one rolled up (and change when its wet), up to the bottom of the window, to collect moisture, when it rolls down, so you do not get anymore sill damage.

It’s only in the bathroom we run the fan during and after shower with the door open also as it’s in the master bedroom. I adjusted the humidistat on the furnace down further then where it was set during install. These are the shades/blinds in there . its the paint not water pooling. So sanding it then repaint the sill?

My guess is this is MDF trim that has absorbed water, best to replace. Certainly seems to be far too much condensation on the window, what is the humidity level in the house?

Yes, damage to the sill makes me think the sill is MDF, too. If it is, then it is a waste of time &

effort w/ sanding & repainting. Hence the suggestion to rip it out & replace it w/ a solid acrylic sill.

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