I use neovim+vimwiki(in markdown mode)+telescope[0] and that setup has been working well for me. I don’t do tags per se but telescope should be able to search those.
Vimwiki does supports tags, and allows multiple tags too. I added a request around 2 years ago to add support for custom delimiters for tags which too was added in the dev branch. I have been a happy user of vimwiki for the last 3-4 years and it works great. Use pandoc for conversion to html, has mathjax support for mathematical expressions along with support for mermaid-js too. For searching the notes i have been using leader-f with fzf, fd and rg.