I want to make the button on the toolbar small because it is large and disturbing.

Creating a lot of checks on a single checklist can cause somewhat slower behavior. This is because the process of updating as many checks as possible occurs. There are parts that depend on the environment you are using, but if you become hundreds or thousands of cases, you may see the phenomenon.

As a solution, you should create a check item divided into multiple checklists. If you divide it into multiple checklists, the load on processing is distributed by that amount, so there is a high possibility that it will be improved.