I play 1.15.2 and notice that creeper explosions destroy the nearby item frames on the walls. It is very frustrating because mob griefing is indeed turned to false using commands and the only long-term solution that might help is to report the issue.
Thank you for your report!
We're actually already tracking this issue in MC-1673, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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