Created attachment 376249 [details]
Contains image of results, HTML to reproduce issue
Using -webkit-background-clip and using transform: rotation has the desired result of clipping and rotating text, but has the side effect of adding a slim 0.5 pixel dashed border. This occurs independent of the font used, so not related to the font. Removing rotation fixes issue. This issue is specific to Webkit Safari both on iPhone and Mac using latest OS. Handles as expected without border in Chrome/Chromium Edge/Firefox.
Work around: use SVG text element instead to achieve the same effect without the border.
Test file attached to reproduce this issue
Created attachment 376333 [details]