With Lift and Shift migrations, the customer could move workloads from a source environment to a target environment with few or no modifications or refactoring

https://cloud.google.com/architecture/migration-to-gcp-getting-started

Reference:
Google Cloud Coldline is a new cold-tier storage for archival data with access frequency of less than once per year. Unlike other cold storage options, Nearline has no delays prior to data access, so now it is the leading solution among competitors.

The key reason I included this question is to clarify some terminologies that will be important for your estimates. The data size mentioned is a TB terabyte. Note the "byte". The speed is mentioned in Mbps, which is Megabits per second. Note the "bits". 8 bits make a byte. So, to get the actual number of bits transferred, you need to multiply the TB number by 8.
Total data transferred (in bits) = 100 * 1,000,000,000,000 * 8 bits
Speed = 100Mbps = 100 * 1,000,000. i.e. 100 million bits are transferred per second.
Hence time taken to transfer all the data = Total Data/Speed = 8,000,000 seconds.
Number of seconds in a day = 24*60*60 = 86,400
Total time taken in days = 8,000,000/86,400 = 92.59 days
Reference link- https://cloud.google.com/architecture/migration-to-google-cloud-transferring-your-large- datasets#online_versus_offline_transfer

Explanation
Because GCP provides three options for paid support which are Standard, Enhanced and Premium.
Basic Support is included with your Google Cloud subscription which cover only Case, phone, and chat support for billing issues only Reference link- https://cloud.google.com/support