At this stage, the Spreadsheet component does not offer support for HTML, subscript and superscript to be typed in, imported from file and displayed in a Spreadsheet cell. That is why, I have converted the following thread to a feature request in our Feedback portal. Based on the support it receives from the community, we will decide on whether to proceed with its implementation or not. I would suggest you to cast your vote for it here.
Regards,
Veselin Tsvetanov
Progress Telerik
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