Restoring iMessages for a friend from my copy

evženfromhavířov wrote:

I forgot to specify; they don't have any backup, neither locally nor on iCloud. That is why I am trying to find other ways for restoring the messages.

Then you screenshot the text thread and text it to them, since they have no backup.

evženfromhavířov wrote:

A friend accidentally deleted their iMessages with me. I still have them, and would like to use my copy to restore the messages on their device — preferably straight in their iMessage app, as if they never deleted them in the first place.

Details: They have iPhone 12, and I do have one of the M1 Pro MacBooks. I have iCloud backup enabled. I trust them fully, so I'm open to whatever it takes that could help them (e.g. logging off my account on my devices and letting them log in).

Thanks a lot!

Your friend would need to restore from their backup Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

evženfromhavířov wrote:

We'd like to restore the full history, hundreds of messages over the last few years. Forwarding or screenshoting is out of question.

Then your friend is SOL since they failed to do a backup of their data.

Have you tried just forwarding the messages back to your friend?