fresh install on mac os big sur
1) after first start slickedit shows first start dialog, where i can select tab/spaces, tab size and braces style (same line/next line). selection in this dialog doesn't affect c/c++ settings - you need to change them manually later.
2) setting syntax indent/indent with tabs/and tab size in options -> all languages -> formatting affects c++ settings only partially
3) i have source file on disk. i'm opening it in slickedit, editing, saving modified code. after this i restoring file's previous state by doing undo multiple times. when edited code in editor window returns to previous state (in which we opened file before) - slickedit marks tab as unchanged (removes 'modified' mark from tab), but on disk file have edited state, which we saved previously after editing.