There are 3 presets for line thickness, but I'd like something custom (specified in mm or pt). It seems that previous excel versions had an option for line thickness when creating a new table style:
Set different borders thickness for the table heading style format
but I can't find it anymore.
21 Answer
You may search "table" on Search bar, then put mouse arrow on Format as Table, click New Table Style.
Select the table element you need, click Format to set border thickness.
If you want to use Line Weight to set table border, please vote up this thread "LINE/BORDER WEIGHT CUSTOMIZABLE". Now this feature could be availble in Word for Microsoft 365 apps, but not in Excel.
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