AI generated area darker than surrounding area

First, are you applying Remove on top of an AI mask, e.g. a Background or Subject mask?  If so, do Settings > Update AI Settings to force the mask to be recomputed, and the difference in tone will go away.

Second, if that's not the issue here, many have observed that the replacements made by Generative Remove sometimes don't match the photo's tone or noise. To get better matches, these techniques sometimes help:

1. Adobe recommends applying Denoise before Remove. This can reduce the noise, making it more likely the replacement will match.

2. The replacement patch supplied by Adobe Firefly has a maximum size of 2048 x 2048 pixels. If the selected area in the photo is larger than that, then the replacement patch gets upscaled (and blurry). Try removing smaller selections if possible.

3. Conversely, try making a larger selection, even including the entire background. Upscaling of the replacement sometimes won't be noticeable then.

4. Sometimes there's a distinctly visible boundary where the tone or noise don't match. You can often use the heal tool around the boundary to get better feathering and make it less noticeable -- apply Heal in small brush strokes. Or use a Brush mask with maximum feathering, dropping local Texture, Clarity, and Sharpness to their minimum values. Sometimes, making a very raggedy selection around the object makes the boundary less noticeable.

5. For grain/noise in particular, see this post for how to ameliorate the problem by adding the grain back or reducing the grain:
https://community.adobe.com/t5/lightroom-classic-discussions/p-generative-remove-feedback-lr-classic-amp-lr-eco/m-p/14917497#M382464

Hi @Jakob35893973xak2 Thank you for reaching out!! 

To achieve the best results with the Generative AI Remove tool in Lightroom Classic, consider the following best practices:

1. Brush Size: Use a brush size that is slightly larger than the object you want to remove. This ensures that you cover the entire object, including any shadows it may cast.
2. Use Detect Objects: Combine the Generative AI feature with the Detect Objects option. This allows Lightroom to automatically detect and mask the object you want to remove, preserving details in the image.
3. Refine Your Selection: After brushing over the object, use the options to add or subtract areas from your selection to refine it further.
4. Review Variations: Once the object is removed, Lightroom will generate three different variations. Review these options and select the one that best fits your image.
5. Overlay Visualization: Use the Show Overlay feature to visualize your selection and ensure accuracy before finalizing the removal.
6. Lighting Cues: When brushing over the object, include any corresponding lighting cues, such as shadows and reflections, for a more natural result.

You may also refer to this Helpx article for more info: Generative Remove - Best Practices and FAQs

Hope this helps!!