The performance of column resizing for locked columns can, indeed, be improved.
In the meantime, I can recommend trying the performance optimization information from this page: https://docs.telerik.com/blazor-ui/troubleshooting/general-issues#slow-performance
Reducing the number of rows on the current page, and the number of columns (perhaps by using column virtualization) is likely to help with the overall performance, not just with the locked columns resizing.
Regards,
Marin Bratanov
Progress Telerik