Look into mumble. It’s NOT a discord replacement but does provide a good quality, low latency, OSS voice chat. Mumble + Signal group chat is what my friends and I use for gaming. Seems to work well.
Tip: Turn on text-to-speech to get narrated announcements when users join channels. Also works for text chat shenanigans. 🤣
I personally use CheckMK.
One thing is that it can be a lot to take in at first and took me a while to get used to it.