Short answer
Any storage that speaks the Amazon S3 API. Amazon S3, Cloudflare R2, Backblaze B2, DigitalOcean Spaces and MinIO have built-in presets, and everything else works through the "Other S3-Compatible" option.
Hosted providers that work through "Other S3-Compatible" include Wasabi, Scaleway Object Storage and Hetzner Object Storage. You enter the provider's S3 endpoint, region, bucket, access keys and the public URL files are served from.
If you run your own S3-compatible server and it only supports path-style URLs (https://server/bucket/key), choose the MinIO preset: it uses path-style addressing, while the other presets use virtual-hosted style.
Step-by-step instructions for each provider are in the setup guides.