Drag on the window split bar is do not work when vim run in tmux

[pangchol]

Describe the bug
Like title, drag on the window split bar is do not work when vim run in tmux.
note:

1. the same system enveriament and same reproduce step flow on tmux with neovim has no this issue.
2. the same system enveriament and same reproduce step flow on bash with vim has no this issue.

To Reproduce

1. Run vim --clean
2. Run set mouse=a
3. Run split
4. try use mouse drag on the window split bar

Expected behavior
the window do not resize when drag mouse

Environment (please complete the following information):

• Vim version [ 8.2.0981]
• OS: [Ubuntu 18.04 LTS]
• Terminal: [tmux 3.1]

Additional context
tmux 3.1 use with default config.

[lacygoill]

I can't reproduce:

Dragging the status line of the top Vim window with the mouse correctly resizes its height.

Try to reproduce on tmux master, and without any tmux config:

$ tmux -Lx -f/dev/null

[k-takata]

Try setting :set ttymouse=sgr.

[pangchol]

Try setting :set ttymouse=sgr.

this settings let mouse drag work fine in tmux, thanks k-takata !