Older version of Garageband will not open newer files

Hi, I have a friend who uses Garageband on an iPhone XR running iOS 18, and we send over files to one another quite often. I use Garageband on an iPad Mini 4, running iPadOS 15.8.3.

Over the past year, we were able to send over files with ease while he was running a previous version of iOS (i couldn’t say which). But now when he transfers files to me, I get an error on Garageband telling me I need to upgrade.

Of course, I cannot upgrade, as Apple lovingly limited the iPad mini 4’s capability up to iPadOS 15. So, is there any way I can still access these files that he sends over? Or do I have no way of collaborating without having to purchase a new device?

Thanks in advance!