On graphene there is no setting that I can find.  I can turn off spell checker but that doesn't help.  I can take away "open supported links" from the keyboard app, but that doesn't help either.  As you back up, when it decides to underline a word, if you back up once more, that is when the space before the word disappears. 

 just use gboard sandboxed 

 Are you sure? It's the standard AOSP keyboard CalyxOS comes with. You should have the same option.
 https://image.nostr.build/b41299ade7fa26fe084ed473d51d0376451dc04321290ce04fc8cd716416e0d0.jpg 

 OK I found it.  There are so many menu paths I looked down before I found this one. It goes like this:
Settings > System > Keyboard > On-screen keyboard > Keyboard > Text correction -> Show correction suggestions OFF