If a word is selected from the suggested text, a space is automatically appended to it on the Samsung keyboard, and the same happens when typing by swipe (glide typing).

"Auto spacing" can be enabled or disabled in the keyboard settings for each individual keyboard language.

Android 10 (One UI 2.0)
Step 1:  Open the  Settings
Step 2:  Tap on  General management
Step 3:  Tap on  Language and input
Step 4:  Tap on  On-screen keyboard
Step 5:  Tap on  Samsung Keyboard
Step 6:  Tap on  Smart typing
Step 7:  Tap on  Auto spacing
Step 8:  Enable or disable  Auto spacing
  1. Open the Settings
  2. Tap on General management
  3. Tap on Language and input
  4. Tap on On-screen keyboard
  5. Tap on Samsung Keyboard
  6. Tap on Smart typing
  7. Tap on Auto spacing
  8. Enable or disable Auto spacing

Samsung Instructions