When browsing the web, you can view images at their original resolution by right-clicking on the image and selecting 'Open image in new tab'. This option will open the image in a separate tab that displays the original upload resolution.
Please see the screenshots below for an example taken from the OCA Library course available on OCA Learn.
If the image can be enlarged further, you will see that your cursor changes to a magnifying glass icon and clicking on the image will zoom in and out.