Download the bus from: https://strefa-omsi.pl/Watek-Scania-Aktiebolag-Citywide-12LF-3D-18LF-4D-Polar-Bear-v0-9-update-24-01-2021--26558 (working download link in post #51)
No need to download and install the patch, it's included
Password for the archive is:
Download and install our patchpack for the bus, that fixes for example 12m version collisions: https://cloud.sepaurg.eu/s/ZReH929RLwQTFNf
Unpack the Vehicles folder from the archive into your OMSI folder. It will ask to overwrite, say Yes.