There are a lot of tools in Tabletop Simulator so you will probably find some things you didn’t know along the way. This is a list of Multi-Selections – some that you probably weren’t even aware of.
To do actions on more than one object at a time (picking up, changing color, grouping, etc), then just hover and drag to box select over objects. They will be highlighted and you can modify them as needed. You can box select up to 128 objects at one time.
Say you box selected a few objects, but forgot to choose a couple. Instead of starting over, you can hold CTRL and then click on each additional object you want to add to your selection.
Additionally, you can deselect objects the same way by CTRL + clicking on them.
If you box selected a bunch of objects and locked them, you may be wondering how you can unlock them without having to do it one at a time. It’s very easy! Just hold ALT and then Box Select around the objects and press L or right click -> Toggles -> lock. Voila!
If you already have objects selected, you can use CTRL + Box Select to invert your selection, while choosing other objects in the process. This lets you select additional objects where you can’t in normal Box Select mode.