Obviously you can delete the styles, one by one, using the Styles & Formatting dialog.
You can right-click on styles in the dialog and choose Edit to see what the properties are.
If you are comfortable editing an XML file, you can dive into the innards of an ODS file and remove the styles; I suspect this may be as slow as using the dialog box in Calc.
You probably know that an .ods file is in fact a zip archive of a number of files; you need to extract the styles.xml file from the top level of the .ods archive; delete from it the entries representing the styles you do not want; and replece the edited styles.xml in the .ods archive. User-defined styles will look like
<style:style style:name="Current_5f_day" style:display-name="Current_day" style:family="table-cell" style:parent-style-name="Default">
<style:text-properties fo:color="#ff3333" fo:font-weight="bold" style:font-weight-asian="normal"/>
</style:style>
I don’t know what the effect of deleting a style that is in use might be, so tread with caution.
If this answer helped you, please accept it by clicking the check mark
to the left and, karma permitting, upvote it. If this resolves your problem, close the question, that will help other people with the same question.