The obvious answer you can find everywhere is:
defaults write .GlobalPreferences com.apple.mouse.scaling -1
which disables mouse acceleration, but locks you at one sensitivity.
Old solutions:
SmoothMouse no longer works. Mouse Acceleration Preferences Pane and SteelSeries ExactMouse both behave the same as com.apple.mouse.scaling -1 at all tracking speed settings (but without restart required).
Is it possible to disable mouse acceleration while still being able to adjust the sensitivity?
Nov 2021: LinearMouse is actively developed & free.
A UI so no terminal messing. It can also help with the scroll wheel acceleration as well.
The built-in options are limited. To achieve your goal a combination of different software could be needed.
Terminal
Like you have already mentioned, the following setting needs to be applied to disable mouse acceleration.
defaults write .GlobalPreferences com.apple.mouse.scaling -1
It can be a good idea to establish a script to automatically perform this action during login to ensure it is properly applied.
Alternatively, mouse acceleration can be configured using SteerMouse (presented below).
SteerMouse
SteerMouse can then be used to adjust your sensitivity. It does require a license, but it also resolves the issue.
Simply download and install the software, either from their homepage or by using e.g. Homebrew:
brew install --cask steermouse
The Cursor settings can then be adjusted to your liking. Acceleration should be left at 0, while sensitivity can be tuned to your preference.
- Speed = ON
Semi-related are also modifications to scrolling which can improve the Mac mouse usage experience.
SmoothScroll
Scrolling with a mouse on macOS can feel unnatural. To improve this one can utilize applications such as SmoothScroll for a better flowing scroll. Further adjustments can be made to customize the speed and related settings to ones need.
It can be downloaded and installed directly from the homepage, or by using e.g. Homebrew:
brew install --cask smoothscroll
Scroll direction
It can be preferential to have different scroll directions between the trackpad and mouse. This can be adjusted in System Preferences -> Mouse. Checking/unchecking Scroll direction: Natural modifies this behavior.
Under Big Sur, defaults write .GlobalPreferences com.apple.mouse.scaling -1 still works but requires a restart. However once restarted and my MacBook Pro goes into sleep mode and comes out of it, the mouse acceleration is back again. It requires a full restart after each time it goes into sleep mode.
Speaking for Big Sur:
CursorSense is capable of this, however it is paid software.
Instead I found https://github.com/docwhat/killmouseaccel which is a free solution that will remove acceleration on a mouse or touchpad, while maintaining the ability to adjust sensitivity.
Launching it on startup is covered well here: https://stackoverflow.com/a/13372744
Not a software solution (and I'm on Big Sur in 2021), so possibly not the answer you were looking for. But, I use a Logitech MX518 Hero which lets you store different DPI profiles physically on the mouse. I mainly use this mouse with Windows (which is where I set all the hardware profiles). But then when I swap over to MacOS machine with KVM, as long as I have the accel disabled via Terminal, then the mouse behaves exactly the same as it does on the Windows machine.
defaults write .GlobalPreferences com.apple.mouse.scaling -1option, alleviates my problem. Really disappointing that a basic feature like this was removed from macOS and the only solutions cost money.