Duck Duck Go's AI suggestion is:

To enable the double space period feature on the Samsung keyboard, go to Settings > General Management > Language and input > On-screen keyboard > Samsung Keyboard > Smart typing, and ensure that the "Auto spacing" option is turned on. If the feature is not working, you may need to reset the keyboard settings to default or clear the keyboard's cache.

EDIT: This (presumably) human, about older versions of the Galaxy:

https://www.techbone.net/samsung/user-manual/auto-punctuate

Tap on Settings

Tap on General management

Tap on Samsung Keyboard settings

Tap on More typing options

Enable or disable Double tap space bar to add period