Twitter will begin phasing out the support for ‘legacy‘ verified accounts and hence will remove the blue checkmarks for those accounts on April 1, 2023.
Legacy Twitter Verified Accounts
Twitter’s goal is to increase the number of people who use Twitter Blue by encouraging them to switch to subscribing for the checkmark.
This may cause some previously verified accounts to upgrade, increasing the number of Twitter Blue users. However, it is expected that the number of accounts switching to Gold checkmark will be much lower.