Let’s back up a bit. 100% is a meaningless term. In Lightroom or any photo app, you work with pixels. Pixels are the size of the recording media (photo sensor) or the display media (computer screen) One pixel of the image is displayed as one pixel on your computer is 100%. Resizing (upsizing or down sizing) is achieved by a translation of the pixels from the source (image file) to the destination media (Screen, print or export file). Normally you do not want to resize on export so your derivative image file will contain the same number of pixels as the original image (or cropped portion). Ignore everything else.
What you are wanting is to display at the best resolution. The best resolution is a factor of your lens quality and the camera sensor. A 300mm telephoto lens is the minimum recommended for birds.
Your cropped image is only 1297pixels wide. If you have a monitor that is 3840 x 2160 or 4K or Ultra High Definition (UHD), then at 100%, your image will take up about 1/3 the width of the screen. This is something that no amount of Lightroom adjusting can alter.
If you use the new Super Resolution function to double the number of pixels, you image at the new 100% will still only be 2/3 of the UHD monitor that I used for comparison.
The things that you can do to improve your resolution is to a) get a better lens b) get a bigger camera with a bigger sensor and more pixels per sensor c) get closer to the subject.
The things that you can do in Lightroom to enhance the resolution that has to exist in the image to begin with is to make use of the following tools: The Texture Tool, the Clarity tool and SuperResolution.
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