Follow the directions here to download your followed contacts from Threads then convert Threads JSON to Mastodon/ Friendica and import your following.json file

Export to: Mastodon Friendica

Convert

On Mastodon, to import go to Preferences>Import and export>Import then Choose File and Upload. Keep it set to merge.
OR go to https://YOURINSTANCEADDRESSHERE/settings/imports

On Friendica, to import go to Settings>Import contacts then Choose File and Save settings
OR go to https://YOURINSTANCEADDRESSHERE/settings/importcontacts

Don't get your hopes up too much though. For my follows, I found less than 5% had enabled ActivityPub sharing.