We want to have only IDs to be shown on the Y - axis in Charts presentation but we see IDs + base64 image strings there (we use them to show images of structures for each ID in Grid view):

Is there a function to customize strings on the Y-axis? I know there is customizeChartElement one but we can change there element which is the bar but not the label. The label hides in data -> rows as a second row:

Hello,
Thank you for writing and providing a detailed explanation.
Given that you need to hide the base64 strings from charts completely, we recommend removing the entire image fields when opening charts. This can be achieved by running methods such as runQuery or setReport with the slice excluding image fields after switching to charts. If you are using default toolbar handlers to switch between grid and charts, you can modify the existing handlers via the beforetoolbarcreated event, as is shown in this example: https://jsfiddle.net/flexmonster/5fb6ay91/
You can use a similar approach to remove the base64 image field when opening charts.
Please let us know if our answer was helpful.
Best regards,
Maksym