There are questions here already about slow loading times for Calc files, but it may be useful to add this one, with some additional data.
I have a simple 254KB .ODS file of IMDB data – text with no calculation – comprising these six sheets in these dimensions:
A: 2342 rows by 12 columns B: 308 x 13 C: 478 x 13 D: 736 x 13 E: 64 x 6 F: 310 x 5
On a desktop system (Win10, Intel i7, 3.4 GHz, 16GB), since installing LO 22.214.171.124 (x64) this file takes approximately 15 seconds to load, during which the window is completely blank except for the outline of the LO icon in the upper left and the Windows actions in the upper right.
The same file, converted with LO Calc to MS Office 365 .XLSX, loads in about 1 second.
On a much older, slower laptop system (Linux Mint 20.1, Intel Core2 Duo, 2.3 GHz, 4GB) with LO 126.96.36.199, the same file in either .ODS or .XLSX format loads in about 3 seconds.
Houston, I think we have a problem.