I use https://github.com/tmuxinator/tmuxinator for my workspaces. Doesn't save ad-hoc layouts, but usually I find one layout that works per project, then create a tmuxinator config for it, so after reboot, it's a short "tmuxinator start $my-project" away to get back to how I want it to be.

https://tmuxp.git-pull.com/ does the same thing, but I think it's smoother to work with. It does support freezing current panes. yaml config