Hi @Nanci Gonzáles, welcome to the Lightroom Community forum! Here are a few steps you can try to troubleshoot the masking issue in Lightroom:
1. Confirm you are in the Masking panel and have selected the correct mask (for example, Subject). When subtracting, click Subtract and select a tool, such as Brush or Linear Gradient. Then, ensure the tool is active before painting.
2. Check that the Masking panel is expanded and you are editing the correct mask layer, not creating a new one by mistake.
3. Make sure your computer and Lightroom are up to date. Then you can restart Lightroom and your Mac.
Please let us know if these steps help or if the problem persists after trying them, and we can continue troubleshooting. I hope this helps! ^CH
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