There is already an established Double Taxation Agreement between MY and Australia
https://phl.hasil.gov.my/pdf/pdfam/AustraliaDTA_20012017.pdf

Article 4
RESIDENCE
1. For the purposes of this Agreement, a person is a resident of one of the Contracting
States:
(a) in the case of Malaysia, if the person is resident in Malaysia for the purposes
of Malaysian tax; and
*Based on your scenario since your wife is in Malaysia more 182 days your wife should be tax resident in Malaysia)*

(b) in the case of Australia, if the person is a resident of Australia for the purposes
of Australian tax.
2. Where by reason of the preceding provisions an individual is a resident of both
Contracting States, then his status shall be determined in accordance with the following
rules:
(a) he shall be deemed to be a resident solely of the Contracting State in which
he has a permanent home available to him;
*Based on your scenario since your wife permanent home is in Malaysia then should be tax resident in Malaysia)*

(b) if he has a permanent home available to him in both Contracting States, or if
he does not have a permanent home available to him in either of them, he shall
be deemed to be a resident solely of the Contracting State in which he has an
habitual abode;
© if he has an habitual abode in both Contracting States, or if he does not have
an habitual abode in either of them, he shall be deemed to be a resident solely
of the Contracting State with which his personal and economic relations are
the closer.
3. In determining for the purposes of paragraph 2 of the Contracting State with which
an individual's personal and economic relations are the closer, the matters to which
regard may be had shall include the citizenship of the individual.
4. Where by reason of the provisions of paragraph 1 a person other than an individual
is a resident of both Contracting States, then it shall be deemed to be a resident solely of
the Contracting State in which its place of effective management is situated.
Article 21
INCOME OF DUAL RESIDENT
Where a person, who by reason of the provisions of paragraph 1 of Article 4 is a resident of both Contracting States but by reason of the provisions of paragraph 2 or 4 of that Article is deemed for the purposes of this Agreement to be a resident solely of one of the Contracting States, derives income from sources in that Contracting State or from sources outside both Contracting States, that income shall be taxable only in that Contracting State.
*(This doesnt apply as your wife is not a dual resident based on the article 4 test)*

Article 23
METHODS OF ELIMINATION OF DOUBLE TAXATION
1. The laws in force in each of the Contracting States shall continue to govern the taxation of income in that Contracting State except where provision to the contrary is made in this Agreement. Where income is subject to tax in both Contracting States, relief from double taxation shall be given in accordance with the following paragraphs.

2. In the case of Malaysia, subject to the provisions of the law of Malaysia regarding the allowance as a credit against Malaysian tax of tax payable in any country other than Malaysia, the amount of Australian tax payable under the law of Australia and in accordance with the provisions of this Agreement, by a resident of Malaysia in respect of income from sources within Australia, shall be allowed as a credit against Malaysian tax payable in respect of such income, but in an amount not exceeding the proportion of Malaysian tax which such income bears to the entire income chargeable to Malaysian
tax.

Basically you need to declare your foreign income received in Malaysia to LHDN then you need to calculate the income tax payable in Malaysia for that foreign income.
If your employer had deducted income tax to Australia Govt before paying you they need to furnish you evidence of the tax paid in Australia so you can deduct that from the income tax payable to LHDN

Example
( Figure are fictional and just illustrative)
Your Foreign Income in Malaysia is Rm 1,000,000
Your MY Income Tax is 24% = RM 240,000
Your foreign employer already deducted RM 180,000 paid as Australia income tax and can provide you with proof
( There should be a EA Form equivalent if your an employee of the Company)
Then you need to declare to LHDN but pay RM 240,000 less RM  180,000 = RM 60,000 to MY Govt

I used to work overseas and was not a tax resident in MY but tax resident in another country. When i return the employer provided full proof of all income tax paid in the foreign country so even if LHDN ask me there is clear trail of evidence. Your scenario is different from me as your a tax resident in MY earning income in AUS so definitely have to declare.

The goal of double taxation is to ensure/minimize the tax resident being tax on the same income from two country ( being taxed twice) that why you are allowed to credit any tax paid in the other country against your income tax in local country.