Can SQL Server Always Encrypted be used for temporary tables?
It appears that you have to create a CMK and CEK in tempdb.

This command Works On My Machine®, and is largely copy/pasted from BOL articles.

USE tempdb

CREATE COLUMN MASTER KEY cmk_whatever
    WITH ( KEY_STORE_PROVIDER_NAME = N'cmk_whatever',
           KEY_PATH = 'Current User/Personal/f2260f28d909d21c642a3d8e0b45a830e79a1420' );

CREATE COLUMN ENCRYPTION KEY cek_whatever
    WITH VALUES
    (
        COLUMN_MASTER_KEY = cmk_whatever,
        ALGORITHM = 'RSA_OAEP',
        ENCRYPTED_VALUE = 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
    );


CREATE TABLE #listofdates
(
    compare_dt DATETIME2(7)
        ENCRYPTED WITH ( COLUMN_ENCRYPTION_KEY = cek_whatever, ENCRYPTION_TYPE = DETERMINISTIC,
                         ALGORITHM = 'AEAD_AES_256_CBC_HMAC_SHA_256' ) NOT NULL
);