Save and load user profiles in QGIS

User Profile Management was added in QGIS v3.0.0. Some information may be found at the GitHub

User profile contains information about the user profile folders on the machine. In QGIS 3 all settings, plugins, etc were moved into a %APPDATA%/profiles folder for each platform. This allows for manage different user profiles per machine vs the single default one that was allowed in the past. A user profile is all settings and anything that used to be found in .qgis3 in the users home folder.

The management tools can be accessed from the Settings menu under User Profiles.

Functionally, this implementation acts in much the same way as the process described in this question and the comments. Loading a new user profile from the menu will open a new instance of QGIS using its associated profile folder.

Merely copying any profile folder to a target installation environment will achieve the migration of settings, but this does not address a "centralized" deployment.

@CrystallineEntity is correct, but more detail below on my Test

Can replace profile settings at least on 1 machine, and I assume others. Used following settings and these moved.

Setup QGIS with various settings, create New profile Settings, User Profiles, New Profile called Default 2
Make a copy of: C:\Users\username\AppData\Roaming\QGIS\QGIS3\profiles And the User Profile, i.e. Default 2

1. Copying the whole profile folder you have modified and then deleting the default profile - WORKS

   On I assume "new" machine/Tested on existing machine with QGIS complete uninstalled
   Install QGIS, open QGIS, set to not import settings
   Go to: C:\Users\username\AppData\Roaming\QGIS\QGIS3\profiles Copy Default 2 the modified user profile
   Open QGIS, got to Settings, User Profiles, select Default 2 All the settings should be there on new profile with Default 2 in title.

   Then delete the standard profile,
   C:\Users\username\AppData\Roaming\QGIS\QGIS3\profiles\default

2. Replace the whole profile folder - WORKS

   Setup QGIS with various settings, make a copy of: C:\Users\username\AppData\Roaming\QGIS\QGIS3\profiles

   On I assume "new" machine/Tested on existing machine with QGIS complete uninstalled
   Delete the \profiles folder, and replace it with the one you modified
   C:\Users\username\AppData\Roaming\QGIS\QGIS3\profiles

Settings
Make changes to Panels/Toolbars, i.e. add Advanced Digitizing Toolbar, remove Browser Panel.
Settings, Options, General, Application, Style (QGIS restart required), Set to Windows
Settings, Options, General, Application, Check QGIS version at startup unticked
Settings, Options, System, SVG Path Set to location on local machine
Settings, Options, Data Sources, Feature and Attributes and table, Representation for Null values: make the box blank, removed the NULL
Settings, Options, Digitizing: Rubberband, Fill Colour, opacity set to 0%

Project, Project Properties, CRS
Searched for the following EPSG numbers, press Apply, Then OK, then repeat for each one.

• WGS 84, EPSG: 4326

• OSGB 1936 / British National Grid, EPSG: 27700

• WGS 84 / Pseudo Mercator, EPSG:3857

Data Source Manager, Vector, Encoding set to utf-8, browse for shp file, press ADD

Identify feature, need to make the Feature title smaller, and make the value box bigger

Plugins, Manage and Install Plugins, search and install MMQGIS
Plugins, Manage and Install Plugins, Installed, Tick MMQGIS and Topology Checker.
MMQGIS option on visible on Menu bar and Topology Checker button visible