Today is 25th February 2022. The first day of the year was a Saturday, so according to the ISO standard -as used by Google calendar etc.) today should be week 8. WEEKNUM System 1 = The week containing January 1 is the first week of the year, and is numbered week 1. System 2 = The week containing the first Thursday of the year is the first week of the year, and is numbered week 1. That means that week number 1 of any year is the week that contains January 4th. ISO 8601 defines this system and that the week starts on Monday. The default is said to be 1, so =WEEKNUM(TODAY()) should return a value of 9, which it does. But =WEEKNUM(TODAY(),2) should return the ISO 8601 number, which is 8. In fact, it also returns 9.
Second parameter Mode argument 2 does *not* denote ISO 8601 week numbering. It specifies that the week starts on Monday for System 1. For ISO 8601 week numbering use either Mode 21 for System 2 or the function ISOWEEKNUM() See https://help.libreoffice.org/latest/en-GB/text/scalc/01/func_weeknum.html?DbPAR=CALC#bm_id3159161