Modern backup systems use reference counting mechanisms, which means you can set up any old versions policy you want. Something like "last 3 annual backups + last 12 monthly ones + last 8 weekly ones + last 30 daily ones" will help a lot against slow encryptors.
You'll want to ensure the malware can't destroy your backup, but that is possible too. A traditional way is to have a separate backup machine that runs backup program and pulls files remotely. Some backup apps can store directly to cloud storage and can work with "append only" permissions, to ensure that client can't delete existing backups. In this configuration, a separate trusted machine must run pruning periodically.
You'll want to ensure the malware can't destroy your backup, but that is possible too. A traditional way is to have a separate backup machine that runs backup program and pulls files remotely. Some backup apps can store directly to cloud storage and can work with "append only" permissions, to ensure that client can't delete existing backups. In this configuration, a separate trusted machine must run pruning periodically.