This is a known issue on MacOS Tahoe:
Problem Capturing Audio
Unable to start audio capture
If the problem persists, try restarting Limitless or contacting support.
We do not currently support recording from the Limitless Mac app on macOS Tahoe (26). Our team is aware of this issue and will be working on a fix in October - November.
In the meantime, you can use the web app. Unfortunately the web app does not support notifications or system audio, however you can record your mic audio.