Effective January 1, 2021 ACBL announced the following changes to Alert rules:
You must now announce minimum suit length promised by 1 of a minor opening, if less than 3. Instead of saying 'Could be short', you now announce the minimum length - 'Could be 2 or Could be 1 or zero'. The exception is 4/4/3/2 distribution so that your 1D bid promises 4 and this is the only time you do it - you do not have to announce or alert it.
You must announce the suit to which you are transferring after 1 NT. Example: Partner1NT - You 2D 'Hearts'. If you transfer to the minors using 2S for either minor, say AlertMinors.
No more alerts for support doubles.
A direct cue bid, after an artificial opening bid, that is not Michaels (both majors over a minor or a major and an unspecified minor over over a major) must be alerted.
Uncontested natural jumpshifts are no longer alerted, no matter the strength shown.
Any 2 Club opening that does not meet the definition of Very Strong requires an alert. If you bid 2C to force a bid from partner and you do not have a VeryStrong hand (as described below), you must alert it.
A Very Strong hand contains -
at least 20 HCP; or
at least 14 HCP and is within one trick of game, assuming suits break evenly among the other hands; or
at least 5 Control Points and is within one trick of game assuming suits break evenly among other hands
The January, 2021 Bridge Bulletin has an article which details these changes on page 35 if you want to read more.