I would like a default MOTD for outdated clients, because sometimes, the downsample RGB Colors look so wrong.

Add an option to disable downsample RGB Colors for outdated clients and enable a "default" motd for outdated clients with default Minecraft colors and formating (no gradient, no RGB)

The config would look something like this:

    # Explanation here
    defaultMotdEnabled: true
    defaultMotd:
     - "<bold><aqua>This is a default MOTD</aqua></bold>"

I was thinking this, I believe there should be a way to use ProtocolLib or ViaVersion to tell which client a player is pinging the server with. And minimotd could use that to determine which motd to show them

As of now, there is no API for this in ViaVersion.

Meaning, this feature as requested would break when used in combination with ViaVersion as ViaVersion will cause the ServerListPingEvent to always report using the server's protocol version, with no way to get the client's actual protocol version.

The reason that all clients reporting as up to date with ViaVersion works fine currently, is that since MiniMOTD believes it is an updated client it sends RGB text, which ViaVersion then internally downsamples using the same API that I do in MiniMOTD.

I see the issue with that. How about without "ViaBackwards" and having a motd for those outdated clients?

You could consider this as well:
arkflame/CleanMOTD#7 (comment)

You could consider this as well:
2LStudios-MC/CleanMotD#7 (comment)

Like is mentioned in the issue you linked, the Via API is useless here, as I do not have a Player object during the ping event on Paper/Bukkit, and like I mentioned before, having Via installed will cause all pings to report to the event as up to date, and Via handles downsampling the colors.

It seems like on Velocity/Bungee the reported protocol version is actually correct even when Via is installed, so it's a possible feature to add for proxies.

You could consider this as well:
2LStudios-MC/CleanMotD#7 (comment)

Like is mentioned in the issue you linked, the Via API is useless here, as I do not have a Player object during the ping event on Paper/Bukkit, and like I mentioned before, having Via installed will cause all pings to report to the event as up to date, and Via handles downsampling the colors.

It seems like on Velocity/Bungee the reported protocol version is actually correct even when Via is installed, so it's a possible feature to add for proxies.

I know this is not very good for design, but I would be very grateful if you implemented this on bungee/waterfall & velocity. This makes it a limited feature but I still think most of the users who use your plugin would appreciate it. I also think anyone investing in a server should look up how proxies can benefit them even if they only use a single server setup 🙂

please add this at least for the proxies