https://gitlab.synchro.net/main/sbbs/-/issues/1141#note_8976

Just a suggestion... I'd start by detecting the position, sending a multi byte character sequence, such as an emoji with skin tone.. then detect the cursor position. This should allow you to determine utf-8 support...

With that you can assume certain upstream terminal support... You can also query/test for rgb color support.
--- SBBSecho 3.37-Linux
* Origin: Vertrauen - [vert/cvs/bbs].synchro.net (1:103/705)

https://gitlab.synchro.net/main/sbbs/-/issues/1141#note_8977

1. SyncTERM doesn't support UTF-8, so I'm not understanding the connection between "Advanced Terminal Type" and UNICODE/UTF-8
2. Synchronet already auto-detects UTF-8 terminals just fine.
--- SBBSecho 3.37-Linux
* Origin: Vertrauen - [vert/cvs/bbs].synchro.net (1:103/705)

https://gitlab.synchro.net/main/sbbs/-/issues/1141#note_10349

I'm also curious how you can query/test for rgb colour support.
--- SBBSecho 3.37-Linux
* Origin: Vertrauen - [vert/cvs/bbs].synchro.net (1:103/705)

https://gitlab.synchro.net/main/sbbs/-/issues/1141#note_10350

The DECRQSS probe — set an odd RGB value, then read back what the terminal actually stored:
Send ESC[48;2;1;2;3m (background to rgb(1,2,3) — no palette entry matches). Send ESC P $ q m ESC \ (DECRQSS request for current SGR).
Read the reply: ESC P 1 $ r <params> m ESC \.
If the params echo 48;2;1;2;3 (or 48:2::1:2:3), you have real truecolor. If they come back as 48;5;n or nothing color-ish, the terminal quantized to the 256-color palette. Reset with ESC[0m after.
--- SBBSecho 3.37-Linux
* Origin: Vertrauen - [vert/cvs/bbs].synchro.net (1:103/705)