GIMP has a set of tools that you can use to edit your images. You can access the tools on the Toolbox which by default lies on the upper-left corner of the GIMP window. If you didn’t use GIMP for a quite while already and have just installed it again on your computer, there is a thing you need to know. Since version 2.10.8, tools in GIMP are grouped. That is why on GIMP 2.10.18 (and maybe the upcoming releases), you will see fewer tools on the Toolbox. A grouped tool has a tiny arrow icon on its bottom-right. You can right-click a grouped tool to see the tool members grouped with it.
The GIMP development team provides no explanation about this change, but big chances are it is intended to simplify the GIMP interface. If you don’t like this change, you can disable the grouping option via the Preferences menu. You can also rearrange the tools order and display more tools on the Toolbox.
Go to Edit -> Preferences to open the Preferences window and click Toolbox under the Interface section. To disable the grouping option, untick the Use tool groups option. The change will apply immediately. Click the OK button before you close the window.
If you find the grouping option useful, you can add a new folder and put some tools to it to group the tools. To create a new folder, simply click the folder icon on the lower side. To add a tool to the folder you have created, you can drag the tool. To delete a folder, you can select the folder you want to delete and click the X icon. To change the order of a tool, you can select the tool you want to change its order and click the arrow icons to put it up or down.
On the bottom section of the Tools Configuration box, you will see some inactive tools. You can enable them by showing the eye icon of each tool.