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I have spell correction on my keyboard, using Heliboard.
As you can see in the screenshot responding your comment, i had a spelling error, underlined with red and the correction suggested above the keyboard:
It's Gboard
Edit: it seems to only work while typing. I opened my comment for editing and errors were not marked anymore.
This community is for people to ask questions they feel stupid for not knowing the answer or how to find the answer. "How do I not already know this?"