lsp-format-mode
lsp-format-mode: per-buffer gate for textDocument/formatting and rangeFormatting — turn it off and `:lsp-format` reports no server for this buffer.
A feature gate, one of the set lsp-mode turns on for you. It carries no keys and no options of its own; what it decides is whether this buffer talks to its language server about textDocument/formatting and rangeFormatting — the request behind :lsp-format.
Why it is a mode rather than a setting
Because it is per buffer, and because it composes. lsp-mode implies the whole set, so attaching a server switches them all on together; turning one off afterwards is a normal mode toggle rather than a special case in the LSP client:
:lsp-format-mode
Toggling it off means :lsp-format reports no server for this buffer. Nothing else about the attachment changes — the server stays running, and every other feature keeps working.
That is the point of splitting the umbrella into gates. A server that is excellent at completion and slow at formatting can be kept, with the slow part switched off for the buffers where it hurts.
Options
None. The mode's presence is the setting.
Keybindings
None of its own.