I tried my code in MacOS 26.0 Beta (25A5279m). The problem is not there, so it seems to be a bug in 15.5. Although this specific issue is fixed in 26.0, it is introducing new ones. The index in the string is clearly being corrupted. I suspect it still has to do between the switch of index between utf8 and utf16. When I type 1234, then press cursor back once, so that curser is between 3 and 4, and type '' three times then I suddenly get '12×3×à 4'. I can see from my log that the input is completely corrupted: input: changed from '' to '1' input: changed from '1' to '12' Moving cursor from 2[any] Moved to 4[utf8] input: changed from '12' to '12×' input: changed from '12×' to '12×3' input: changed from '12×3' to '12×34' Moving cursor from 4[utf16] Moved to 7[utf8] input: changed from '12×34' to '12×3×4' Moving cursor from 7[utf8] Moved to 8[utf8] input: changed from '12×3×4' to '12×3××4' Moving cursor from 8[utf8] Moved to 9[utf8] input: changed from '12×3××4' to '12×3×\303×\2274' code-block It seems that the text selection in TextField is not great yet. I wanted to raise a developer support but it said that apple engineers will prioritise forums during this time. Hopefully someone can take a look at this. I also tried changing from String to AttributedString to test the new TextField with formatting but this does not seem to be available yet.

This issue is now fixed in macOS Tahoe (26.0 (25A353))