Has the 'iddah (waiting period) of the divorced woman who has not menstruated for four months, except for two cycles, expired? And is the suitor sinful for proposing to her and entering her house in this situation?

An irregular menstrual cycle does not prevent the completion of the iddah (waiting period). Therefore, you should wait for the third menstruation. If it is delayed without a specific reason, you should not end the iddah except after a year has passed, starting from the date of your last menstruation. This is based on the saying of Umar (may Allah be pleased with him): "She should wait nine months. If pregnancy is not apparent, she should observe an iddah of three months, making it a year in total." You are currently in the iddah of divorce, and your ex-husband can take you back if the divorce was revocable (raji). It is not permissible for any other man to propose to you explicitly if the divorce was irrevocable (ba'in), nor implicitly if it was revocable (raji), before the iddah ends, based on the verse: "And there is no blame upon you for what you allude to concerning a proposal to women..." (2:235). This is because an explicit proposal might lead to falsehood regarding the expiration of the iddah.