The manual really is your friend! I believe all of this is also covered in the excellent getting started video.
to stop looping, just press loop. to clear the section of tape occupied by the loop, press record+down to engage overwrite recording (both lights above record lit). recording nothing / silence will erase the tape.
Here I believe there is still a typo in the manual, but it’s correct on the reference card. if you enter cue mode (white light above the toggle) by pressing loop and record and navigate with the toggle or loop+up/down to the new cue point you added, the light above record will be orange. pressing record will delete the cue point, which you can confirm by noticing the light above record swaps to white.
currently your best bet to remove all cue points without clearing the audio is to enter cue mode, and then press record a bunch of times—this will alternate between deleting the cue point you’re at and moving a cue point to where you are for deletion
holding down in nav mode (only orange light above the toggle) will rewind and progressively speed up, just like on a tape recorder. If you hold down and then press play, you’ll latch into live mode with reverse playback, at which point the usual play+up/down will double or halve playback speed, respectively.
As you can see above, this is a known issue where the SD card driver crashes. A fix is in the works