You want to know the limit on how many Deny or Allow list entries that Endpoint Detection and Response will accept.
SEDR version 4.1 and later will allow you to have 65,000 total entries in the Deny list or Allow list. You will not be allowed to use more than 65,000 entries in your lists and an error will show stating that the policy limit is reached when attempting to add any more entries than the 65,000 limit.
As of version 4.5 the blacklist and whitelist names were updated to Deny list and Allow list.