I'm with Krissie put another piece of moulding over it. Perhaps a 14/ round piece added to the top of the door. If this is an aesthetic repair, IMHO filling a gap like that with flexible caulking won't look good. That being said, if it's not aesthetic (you can't see it normally but need to get on a tool or something to see the top of the soor frame) then what difference does it make? Leave it and forget about it. Lastly, you could remove the top molding, cut out a piece of the drywall and replace with a piece that will fit nicely to the frame, finish the drywall joints, paint the wall and replace the molding. "filler" is not a good solution. Just my 0.02.

Thx yes was going look around the control valve next. Looks to me that the tile has not been routinely maintained (sealed). So some aging and cracking in grout may have added to the problem. Been in the house two years with no visible issues with daily use, it looked perfect (e.g. no staining in bottom grout until suddenly now). This disscussion really makes me wonder about the way tubs are sealed to walls. A Silicon seal acting like a ~1/4" water dike trapping and holding water makes no sense. Seems to me that there should be a 1/2" gap under the wall backboard with current recommended water barrier behind extended 1/4" further overlapping the tub flange. And their should be engineered a flexible polymer strip to be inserted in the gap to seal between the tub ledge and the tile. It should have antimicrobials in it and be treated annually with an application of antimicrobial treatment. The invention could be a firm microbubble nondegradable polymer. And it should have a GoreTex film like property, where free water can't get across it, very little moisture is held so it dries quickly, and moisture settling behind the bottom tile can excape as water vapor. Slight permeability to the flexible material and a fused backing of the Goretex oriented towards the flange wall could accomplish this. It could have a thin flap on the back topside so it is installed along with the bottom tile and act as the standard 1/8" spacer below the bottom tile. Being flexible and supported from the back edge it could flex downward if the tub ledge moves downward when weight loaded, still helping block water entry. If the tub settles a little permanently, the permeable membrane would still help block transport water out of the gap. A spongy expandable sealed bubble like strip material would allow the most water blockage with flexing and also be best at preventing any air gap developing. Just an idea ... on my wish list.

@live_wire_oak and @weedmeister thanks for the tip. Looks like the Costco installer was an amateur. I asked him the exact same question and he mentioned the grates will be aligned and not the top of the stove. He also never checked the level. I guess I will call them and ask if they can send someone more knowledgeable over. For the back it says 1inch gap is enough but who knows, looks like no one knows what they are doing anymore. Also, I am hoping that once I install the microwave on top the vent will be pretty good and quickly remove any heat. @wacokid yeah I wish I never asked the question about cooktop + wall oven below the cooktop (instead of raised in the wall) on Houzz. After hearing it is not a popular combo in the US, I decided to demolish my current setup and change. Big mistake! Thanks for the filler options @Shannon_WI.

This is above the tub/shower. Again, he didn't do the waterproofing and I am confident the corner is well sealed behind the tile (goboard, goboard sealant, fibertape embedded in hydroban) but I still thought he would have run the tiles closer, as I can see the goboard behind it the tile. I assume the latasil caulk here is all that is needed. I just don't know if this is the way most do the corners in walls. all of the corners have gaps. Maybe this is the expansion joint that EJ 171 is referring to and supposed to be a gap?