With LMDE5, whether with the live ISO or a full-updated installation, the default mouse cursor pointer is not always white with a black outline - in some programs, it inverts to a black cursor with a white outline.
The easiest way to test this is to simply open a video file in Celluloid and put your mouse cursor on top of the video image area - you'll see that your mouse cursor pointer's color will invert.
Going into LMDE5's "Themes" settings and re-selecting the 'Mouse pointer' as "DMZ-white" fixes the issue.
Also note that Mint 20.3 Cinnamon does not have this issue.
With LMDE5, whether with the live ISO or a full-updated installation, the default mouse cursor pointer is not always white with a black outline - in some programs, it inverts to a black cursor with a white outline.
The easiest way to test this is to simply open a video file in Celluloid and put your mouse cursor on top of the video image area - you'll see that your mouse cursor pointer's color will invert.
Going into LMDE5's "Themes" settings and re-selecting the 'Mouse pointer' as "DMZ-white" fixes the issue.
Also note that Mint 20.3 Cinnamon does not have this issue.