Best way to back up databases on a Microsoft SQL Server Availability Group DR Site node
You can use some system dynamic management views (DMVs) and functions in your backup script, for example:

sys.dm_hadr_availability_replica_states
sys.fn_hadr_backup_is_preferred_replica
sys.availability_databases_cluster
sys.dm_database_encryption_keys

to determine the current node's assignment (primary, secondary, etc) and direct where the full/diff/t-log backups should be coming from. If you use that in conjunction with a file share (as @Steve mentioned), then all backups can be pointed to the same target. You can get creative from there (eg, copying the backup files from the share to another site) to bolster for DR purposes, etc.
You may also glean some good script setup insights from Ola Hallengren's backup scripts (https://ola.hallengren.com) which take AGs into consideration.
Hopefully that helps some.