When selected as a plain text, not markdown in the per note options, a tab character precepts as an indent for the entire line if a - (hyphen) is at the start of the line. Any subsequent use of tab on the same line only adds another indent to the line rather than where it is located on the line.
This behavior is inconsistent with plain text rules and rather commonly that of markdown.
Windows Version: 11 24H2
Simplenote Version: 2.23.2.