Connect Single 3-way Light in 3-gang Box (Lutron Caseta)
The first thing you do is roll it all back to status quo ante with the original switches and get it back where it works 100%.
Now you'll see a black wire that is split to go to at least 2 switches. (it may pogo from switch to switch).   We're not worried about that one for now, but its function is always-hot.  We'll be spending most of our time with the other wire on each switch.
The outdoor light
On the outdoor light, pull the (remaining) wire off the switch that controls it, and cap it off for good.  It's done.
Identify the neutral wire that is the partner to this hot, and make a mental note to cap it off also, later.
Hot or not
Notice that the 3-way switch has 2 brass and 1 black screw.   The 2 brass screws are the travelers.  3-way circuits work by making one traveler hot and the other traveler not hot.
Pick a brass screw and take the traveler wire off it.  Cap that wire off for good.  It's done.
Now, take the traveler wire on the other brass screw, and wire nut it to the (common) wire(s) on the black screw.
See what we did there?  We made the first traveler not and the other traveler hot.
That's it; the 3-way switch goes away.
The kitchen switch
This Lutron switch is neutral-less, which is unfortunate because you seem to have neutral present, and this choice will require you to add an additional module called a LUT-MLC to effectively simulate neutral.
At this point one wire remains (that isn't capped or always-hot).
Now we take that single wire and join it to two things: a) one of the black wires on the Lutron switch, and b) one of the two wires on the LUT-MLC module.  So 3 wires come together.
The other wire on the LUT-MLC module gets added to the bundle of neutral wires.  While you have that bundle apart, remove for good the neutral that is the partner to the outside light you just capped off.
The remaining black wire on the Lutron smart switch needs to be added to the &quot;Always-hot&quot; bundle.  This is a good time to get rid of any unused pigtails etc.
Lastly the ground wire must be added to the ground bundle.