There is a 1.6 plugin for this released by
Solstice:
https://community.mybb.com/thread-69096.html
but looks like it was been abandoned already and might not be compatible with 1.8
I found almost similar thing it does for 1.8 which is this one:
[For 1.8] Hide Thread Content by snlbaral
Hides Thread Content until user replies to the thread.
If possible i am looking for mybb 1.8 plugin where in instead of forcing user to reply on a thread,
just ask the user to press or click the [thank] button and the content will be unlocked.
Willing to pay for this kind of plugin. Thanks. 
--> even user quote the content, the content we hide wont be unlock, it will only be unlock by pressing thanks.
--> after pressing thanks, it will be unlock without the need to refresh cause on 1.6 version where in it uses Ajax, after pressing thanks, we need to manually refresh it to unlock the content, if possible if it auto refresh after clicking thanks button.
Willing to pay for this kind of plugin. Thanks.
Sorry for this off-subject answer, but I want to give a personal opinion about this kind of functionments: I can't understand why an user must thanks or reply before having read (or download in most cases).
Is it a race to thanks/answers ?
I prefer when an user sincerely likes a post rather to force him to perform an action before being able to have the entire content.
My 2 cents.
If a thank you is logged, it will give you a history of who clicked to read.
Not sure why you'd want to do that, but that's one result.
(2023-01-04, 02:35 PM)Crazycat Wrote: [ -> ]Sorry for this off-subject answer, but I want to give a personal opinion about this kind of functionments: I can't understand why an user must thanks or reply before having read (or download in most cases).
Is it a race to thanks/answers ?
I prefer when an user sincerely likes a post rather to force him to perform an action before being able to have the entire content.
My 2 cents.
Thank you Crazycat for that comment.
I already used plugin that "force to reply user to view or unlock the thread" and somehow the forum will be filled with spam post from users who wanted to unlock the thread, that is why i am looking for a thank you plugin where in users are not force to reply, but they will only be force to click the "thanks button", reason for asking this kind of plugin are some of the user/sharer that when they post/share something it will be leecher free and also to protect the content from leecher.
Member(s) complain they start a thread then an hour ago it was reposted on other site already without credits, so plugin like that would be good in protecting content somehow from leecher. Thanks.
cause before on mybb 1.6 the plugin by Solstice:
https://community.mybb.com/thread-69096.html
had been so much helpful in finding members who just leeched content that even OP (original poster) can easily spot among members that possible leak the content, especially if the thread starter does not wanted it to be shared or posted elsewhere.
(2023-01-05, 02:07 AM)HLFadmin Wrote: [ -> ]If a thank you is logged, it will give you a history of who clicked to read.
Not sure why you'd want to do that, but that's one result.
Hi HLFadmin, thank you on the reply. Did you have a working plugin like that which is working on mybb 1.8? Thanks.
You can try
https://community.mybb.com/mods.php?action=view&pid=67
It uses the system to hide the content inside hide tags by default, you can change it at your owns but only shows the content inside that tags, i was written a feature like that for some forums while ago i can remember it was many years ago but it can be improved in some way like that. You have not to use more than one plugin for it but imo it is better if you show some parts of the content and only relevant parts must be hidden inside tags to allow user to thank and do not force to thank and unthank due this plugin can allow you to unthank and if you use the setting only can thank, that way is best for no spammers and have the antispam and some other features aswell. It is an old mod but i suppose it works without problems in the last mybb versions.