Also worth checking out is The Archive. There are some differences, but I've been very happy with it as a successor. https://zettelkasten.de/the-archive/
The Archive is great! NValt is also wonderful.
I use Archive for a true Zettelkasten and nValt for meeting notes.
nvUltra is still in beta. nvALT still works (Big Sur too) but hasn't been actively maintained.
I've been experimenting with FSnotes[0] lately and find it be be the closest an app has come to the simplicity of nvALT