using Libre with a reasonably big spreadsheet - 600kb in 123 file type. 12000 cells. Its clunky taking lots of time to save and to edit. Should be plenty of capacity in the PC but it does seem to be in part at least a memory /cache issue. If I save and continue, for a short time the processing is slick again and then rapidly slows. Memory is 8gb which is about 50% used. SSD and HDD are way less than 10% used. Only thing I can see is the L1 cache is about 288kb whatever L1 is.
no different if I save in ods.