Another way is to programmatically work with the REST API and export the needed data (https://docs.gitlab.com/ee/api/). This can be needed to specific backup and persistence routines for data compliance too. I personally recommend to use the Python, Ruby, etc. library bindings for easier API requests.
This won't solve the import into another tool, yet it opens a migration possibility with full access via an API.
While we do not want you to leave ... :-) ... you'll have great tools to export your data from projects, for example https://docs.gitlab.com/ee/user/project/settings/import_expo...
Another way is to programmatically work with the REST API and export the needed data (https://docs.gitlab.com/ee/api/). This can be needed to specific backup and persistence routines for data compliance too. I personally recommend to use the Python, Ruby, etc. library bindings for easier API requests.
This won't solve the import into another tool, yet it opens a migration possibility with full access via an API.