https://help.twitter.com/en/rules-and-policies/inactive-twitter-accounts
What is Twitter's inactive account policy?
We encourage people to actively log in and use Twitter when they register an account. To keep your account active, be sure to log in at least every 6 months. Accounts may be permanently removed due to prolonged inactivity.
How does Twitter determine inactivity?
Inactivity is based on logging in. Please note that you may not be able to tell whether an account is currently inactive, as not all signs of account activity are publicly visible.