Rule 235 “Trier of fact” includes (a) the jury and (b) the court when the court is trying an issue of fact other than one relating to the admissibility of evid…

The "trier of fact" is whoever decides what actually happened in a case. That is either a jury or a judge, depending on how the case is set up.

When there is no jury, the judge takes on both jobs: deciding what evidence is allowed in court and deciding the facts of the case. But when this rule says "trier of fact," it only means the judge acting in that second role, when weighing the facts to reach a verdict.