  We demonstrate the existence of topological phase transitions in interacting,
symmetry-protected quantum matter at finite temperatures. Using a combined
numerical and analytical approach, we study a one-dimensional
Su-Schrieffer-Heeger model with added Hubbard interactions, where no
thermodynamic phase transition occurs at finite temperatures. The transition is
signalled by a quantized, non-local bulk topological order parameter. It is
driven by defects, which are enabled by the combination of interaction and
thermal activation, with no counterpart in the non-interacting limit. The
defects localize topological zero modes, which, when sufficiently abundant,
cause the order parameter to vanish. This phenomenon, interpreted via
bulk-boundary correspondence, reflects the loss of a topological edge mode at a
well-defined critical temperature in the thermodynamic limit. Unlike
zero-temperature topological transitions, these finite-temperature transitions
lack thermodynamic signatures but remain observable in controlled quantum
systems, such as ultracold fermionic atoms in optical lattices.
