Testing QNEAT3 with QGIS 3.99.0 (and QT 6.9.2), i've experienced an error when QNEAT3 call QgsVectorLayerDirector with enum value as int and not as QgsVectorLayerDirector.Direction enum for default Direction.
I propose a PR that solve this point and present a QNEAT3 ready for QGIS4 but only tested on linux Voyager V25 and a QGIS 3.99.0
My tests are not exhaustive but concerned all "OD-matrix xxx"