This is normal behavior. The algorithm may take seconds to minutes to build an impulse response depending on the render resolution and the number of reflections in the rendered scene. To speed up IR generation, try rendering at a smaller resolution. Larger resolutions "catch" more reflections and thus allow for more lush-sounding reverb, but there always comes a point where more pixels is overkill because it basically sounds the same. Smaller resolutions can still produce good-sounding reverbs, depending on the size of your scene (bigger rooms generally need higher resolutions for more reflections to fill out their longer reverb tails).

Starting in Blender 4.2, extensions are the new way of doing add-ons and themes. Legacy add-ons are considered deprecated but continue to be supported. See Here: https://docs.blender.org/manual/en/4.2/advanced/extensions/addons.html#legacy-vs-extension-add-ons If you are on a version of Blender older than 4.2, the legacy add-on is the one to download. Installation Instructions: https://cgmeerkat.readthedocs.io/en/latest/addons_installation.html CycleAcoustics is built as an extension and a legacy add-on in order to support more Blender versions. CycleAcoustics’s features do not differ between its legacy and extension variants.