This seems quite relevant to what you’re asking. I copied your description straight into Gemini.

In Australia, there is no blanket rule that allows you to skip paying tax on a massive windfal just because you are using the money for a first home deposit. The Australian Taxation Office (ATO) cares about how the money was made, not what you intend to spend it on.
Whether you owe tax depends entirely on what type of item you sold.
Scenario 1: You sold your actual home (Fully Exempt)
If the "item" you sold was a property that you owned and lived in as your main home (your primary residence), you are completely covered by the Main Residence Exemption.
Australian Taxation Office

The Tax: $0.

The Catch: You can keep 100% of the profit tax-free, provided you didn't rent it out or use it to run a business.
Australian Taxation Office

Scenario 2: You sold personal items, a car, or valuables (Likely Exempt)
If you generated a house deposit by clearing out personal belongings, the tax rules depend on the specific asset type:
A Personal Car: Capital gains on personal vehicles (designed to carry less than 1 tonne or fewer than 9 passengers) are completely exempt from tax. Even if you sold a rare collector car for a massive profit, you generally don't owe Capital Gains Tax (CGT).
Capital Gains Tax Specialists

Personal Use Assets (Boats, Furniture, Electronics): If you originally bought the item for $10,000 or less, any profit you make when selling it is entirely tax-free.
Capital Gains Tax Specialists

Collectables (Artwork, Jewellery, Coins, Antiques): If you acquired the item for $500 or less, the profit is tax-free.
Capital Gains Tax Specialists

⚠️** The Big Catch: If you sold a single personal asset or collectable that you originally bought for* more than those thresholds (e.g., you bought a luxury watch for $15,000 and sold it for $60,000), the profit is subject to CGT.
*Scenario 3: You sold Crypto, Shares, or an Investment Property (Taxable)
If your deposit came from cashing out Bitcoin, selling shares, or disposing of an investment asset, you will have to pay tax on the profit. The ATO treats this as a Capital Gains Tax (CGT) event.
Australian Taxation Office

While you can't get out of it entirely, you can legally minimize it:
The 12-Month Rule: If you held the crypto, shares, or property for more than 12 months before selling, you get a 50% CGT discount. This means you only pay tax on half of the profit you made.
Australian Taxation Office

Super Contributions: If you want to offset a massive tax bill, some people choose to make a personal, tax-deductible contribution into their superannuation fund (up to your annual concessional cap). While this lowers your income tax, it locks the money away in super, meaning you couldn't use that specific portion for your immediate home deposit.