What I like about Tabby is the fact that it has also options to connect to serial ports.

I know that is not something useful to everyone, but working in an embedded using serial ports is something I do everyday. And I know there is Putty or Kitty or Teraterm or another serial connection tools, but most of them are either only for Windows, and don't allow all the options that I need (e.g. option to enable local line editing with history).

The fact that it uses Electron... whatever, we are still full of Electron applications anyway, it's not an issue to me, I have enough RAM.

I've jet to find something replacement that either has all the features of tabby (including support for connecting to serial ports) I would be happy to switch.

Just use picocom in any terminal you like: https://github.com/npat-efault/picocom (unmaintained, but works fine and there is a ng fork: https://picocom-ng.oddbit.com/). Or minicom or screen, but those are more bloated.

There is little reason for SSH client to be integrated into a terminal emulator. Admittedly, my favorite kitty has a wrapper around OpenSSH, to fix terminfo and stuff, but it doesn't tries to re-implement the protocol. There is even less reason for serial port terminal to be a part of a terminal emulator - serial port terminal simply sets baudrate, remaps some control characters and gives you an escape key, it is not connected to rendering in any way.