Hi there, I have different computers and operating systems to run (Win 11, 10, 8, 7-32&64, and Linux Mint 19-22 and Ubuntu). Seems my used Cryptomator version is rather old (1.5.17) but it has been running on both Linux and Windows.
They next version (1.6) already denies Win7. I tried in Win 10 and I could open my old data container. But seems it updated and there is no way back.
Now my question, is there an interchange format or procedure or best practice? I would love to use all the new versions and feature until recent version but what about my data? Is there a defined upgrade/downgrade process? As far as I know, most software in the world provides data compatibilty.
Welcome to the Cryptomator community 
There is a defined upgrade process, but no downgrade process. Once a Cryptomator vault is migrated to a newer version/vault format, you cannot open it with an older Cryptomator version.
That said, between vault format 7 and 8 only the metadata changed. So, what you could do is save a copy the vault-format-7-masterkey and migrate the vault to format 8. If you want to open the vault with an 1.5.x Cryptomator version, rename the saved format-7-masterkey to masterkey.cryptomator. If you want to open the vault with a 1.6.x or higher Cryptomator version, rename the format-8-masterkey to masterkey.cryptomator.
Please keep in mind, that this is a brittle setup and this might break with the next vautl format update.
Thank you so much. You’re my cryptomator hero 
Also keep in mind that such old software contains many unclosed vulnerabilities and bugs. We therefore strongly recommend that you always update to the latest version in order to benefit from all fixes.