the new gamertag freed up policy

They won't do another mass release of gamertags. They changed the policy in 2016 and if a person doesn't sign into their Xbox account within 5 years, the gamertag will be freed up. As of 2019, if a person doesn't sign into their Microsoft account within 2 years, the account will be closed which should also free up the tag. However, they also created a new gamertag policy in 2019 so you can use the same gamertag as someone else, you will just be given a suffix to differentiate the 2 accounts. So if you're looking to have the tag without the suffix, then the original tag would have to be freed up and no one else using it.

Gamertags are used on other services so just because it has 0 gamerscore does not mean it isn't being used.

Due to policy changes made in Aug 2016 if a gamertag does not sign in for 5 years it is then it may be freed up & as of 2019 if a Microsoft account does not sign in for 2 years that may be freed up so either way the earliest any unused gamertag may be freed
up is around Aug 2021 but even then it's not guaranteed.

There's no way to no if/when a gamertag will be freed up. Starting August 30, Microsoft accounts will be closed if they are inactive for 2 years so assuming the person who has it is not actually using their account at all, it would be freed up as part
of that. Otherwise, they would have to change their tag to something else in order to free it up earlier than that. As XBF Eladio mentioned, there is a new gamertag policy in place so you could still have the same gamertag, there would just be numbers added
to the end to distinguish between your account and the original.

After some policy changes, there will not be another mass reset. As of 2016, if a person doesn't sign into their Xbox account for 5 years, the account will be freed up. As of August 30, 2019, if a person doesn't sign into their Microsoft account within
2 years, the account will be closed which should free up the gamertag as well. Otherwise, with the new gamertag policy, multiple people can use the same gamertag, you'll just be given a suffix to differentiate between tags.

MS new policy Starting I believe right after the last time they freed up a bunch of gamertags about 2 years ago was to start freeing up gamertags that are inactive after 5 years and that 5 years started from the new implementation of the policy.

Keep this in mind this means that the account that the gamertag is attached to can not be signed into ANYTHING to do with MS so if the account is attached to a windows 10 computer, an office subscription or anything else besides xbox to do with MS then that
counts as being active.