Is there any android client rather than using the web-interface that firefox wont let me connect to remotely without a valid certificat.
No, I use the PWA, i.e. access the page on your phone and as long as it's https it will prompt you to install it. Personally I just used a tailscale network to get past the https authorisation, this also allows me to access it outside of my house so win-win
While it looks easy to use markup language using /, I'm wondering is there is a plugin that add a tool bar or a client app that does have it.
Didn't understood, this is just a markdown file, you can just type things, no need to have buttons to add text.