I accidentally reacted to a message on Messenger

To change your reaction to a post or comment, tap and hold your current reaction (next to Comment and Share), and then select a new one. To remove your reaction to a post or comment, tap your current reaction. Was this helpful?

In Facebook Messenger, if I "react" to a chat message and then remove the react soon after (within 20 seconds) will the other person still get the notification that I reacted to their message if they're offline? Yes. Its like when you like something then unlike it , they still receive the notification.

No. No notification will be sent if you delete a reaction. In fact, if the person never saw the message, they wouldn't know if you reacted and then deleted the reaction.

The person who would receive the message can't see you deleted it for yourself.