I used stud finder...they are only at one inch outside of the trim

There should be a header there, so should be solid wood above the window. All windows should have a header.

It's hard to believe that there aren't any studs above the window. Sometimes those stud finders can give false results - especially if not used correctly.

If there is no solid header in the wall above the window:

Instead of nailing two individual wood blocks, use one strip of wood (like a 1x3) snugged up to the top of the casing that is long enough to be able to nail into the studs that are on each side of the window. Or the same length as the horizontal casing. Paint to match the trim and attach the shade wherever you need to on the added strip.

The shade should cover this added strip.

Header as cat_ky said, but I would cut the blind to fit inside the casing.

Can I liquid nails + nail gun the board? Is that sturdy enough without studs?

" Can I liquid nails + nail gun the board? Is that sturdy enough without studs? "

No, a block of wood needs to be attached into wood. The blind brackets themselves can be installed in drywall with anchors however

The blind brackets can't be installed with anchors bc then blinds will go down on angle bc of the trim below it

Ask if the blinds manufacturer has a spacer for this purpose. Mine came with a small piece that worked with a drywall anchor and allowed the blinds to sit above the window and avoid that bump from the trim.

“The blind brackets can't be installed with anchors bc then blinds will go down on angle bc of the trim below it”

Step 1: Attach the wood blocks on the wall with two-sided tape.

Step 2: Locate the proper holes for the blinds.

Step 3: Drill the holes through the wood and into the wall. Take your time and try to keep your drill level.

Step 4: Go to the big box hardware store and buy screws that are 1/2” - 3/4” longer than the ones provided with the anchors. It wouldn’t hurt to buy beefier anchors also since the ones provided are not really designed to support the extra protrusion.

Step 5: Remove the blocks and pound in the anchors.

Step 6: Attach the blinds to the blocks and the wall with the longer screws. This part is going to be annoying but not hard.

Note: You really want to do step 4 first.

Alternatively, just attach the block with anchors and the blinds with wood screws, making sure your anchors and screws will not interfere with each other. Again, I would use beefier anchors.

Before doing any of that, take a long finish nail and test where the blocks will go - just hammer it in enough until you feel something solid, then remove it. If there is no wood, then the nail will punch through the drywall very easily and you can pull it back out with your fingers. But you should find a wood header there, which means you do not have/cannot use anchors.

Just because your stud finder isnt finding anything, does not mean there is nothing there. There has to be support there. Usually its a header. That header may be nailed to studs, on left and right of window, it may not have any nails in that area. A stud finder finds nails, to alert you of a stud. It doesnt find all 2x4s and studs, if you are not in an area where it would be nailed. Put a nail in there and see if you hit something.

@Stax you just said "there are studs" but the OP clearly knows the stud finder did not find any. That is because when sliding the stud finder sideways starting next to the window, the alert will register at the King Stud, but will remain on if you keep moving it across the header instead of registering multiple stud cavities, so it seems as if there is no wood up there. If you start the stud finder above the window at the header and move it sideways, it will not give an alert because there is no cavity to register.

Since it's an exterior window, there is certainly a header. Only with high ceilings would the stud finder find any cripples, or in Canada sometimes the header is put flush to the top plate and cripples are below that. Another situation is a 2x6 wall where the framer left an open cavity above the window from only a double header, but the nail test method will find out everything.

I tried. I give up!

Well....I put a nail through and it did hit something a little bit deeper in that wasnt drywall. However, when I tried to put in a long screw it just wouldn't grab onto it. It's like if I was screwing into steel. Regardless, I went the nail gun route and it seems to be very sturdy. Thanks everyone for your input. If it fails, I will let you know!