Since the recent update of "pale garden", that constant ambient sound of the Nether cant be heard while the "True realism pack" is active, both in new and already created worlds.
Only blocks and nobs make sounds, basically is like being in Overworld, where there's no constant ambient sound.
When disabled the pack, sounds can be heard like normal.
Thank you for your report!
However, this issue is Invalid.
Unfortunately, we don't accept issues related to third-party Marketplace content here on the bug tracker, but you may wish to contact the content creator directly. Please visit this article for information on how to contact the content creator.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support (Technical Issues) – 📧 Microsoft Support (Account Issues)
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki