Is this Laptop worth $900 and can it run games decently?

Is it worth 900$? Not used without warranty. These were sold recently for 999.- € at Aldi in Germany (German link, but computer psecs are computer specs).

Cam it run modern games decently? Probably yes, depending on the game, screen resolution and what you understand as "decently".

Most of the Lenovo Y530 have GTX 1050 TI. Rank 106 for GTX 1050 TI and #126 For GTX 1050 on this table of gaming to graphics processing

i7-8750H is a high performance CPU, score 12,407

It will run all games, newest ones on lower game settings and anything over a couple of years old on high settings. Laptops run gaming on AC power plugged in and the laptop must be on a hard surface for ventilation.
At Mwave, that should be the best pricing in Australia,
$1200 ASUS TUF Gaming FX505DT 15.6" 120Hz Gaming Laptop R7-3750H 8GB 512GB GTX1650
The AMD Ryzen 7 3750H scores about 9000 so is not as fast as the i7 of the Lenovo, but the GTX 1650 is stronger at rank #77, and a 512GB SSD stores less than the 1TBHDD/128GBSSD Lenovo, but 512GB SSD is good also

By $1400 this MSI has better specs than the Lenovo by a bit
https://www.mwave.com.au/product/msi-gl63-8rds-156-gaming-laptop-i78750h-8gb-512gb-gtx1050ti-w10home-ac24816
You can say that the Lenovo in new condition should sell for $1300. The Asus at $1200 with AMD CPU is also a comparable.
AU$900 is a OK price, since JW wants $1244 for similar, but MWave beats jw.https://www.jw.com.au/ex-demo-msi-gl63-8rcs-051au-15-6-gaming-laptop-i7-8750h-8gb-ram-512gb-ssd-gtx1050-windows-10-home

That computer will be able to run every game available just fine at 1080p with moderate settings. It would have about the same specs as a regular ps4 or xbox one. For $600 USD it's a good price for something like that.

If the laptop is in good physical condition and the system has not been abused with overclocking and other nonsense then it's a good buy. It is possible to purchase similar systems for a couple hundred extra and I, personally, prefer to purchase computers new as I'll know the history behind it.

A lot of people like to overclock and fiddle with their computers and then when it does not work out, they sell it without indicating what problems they had or what they did.

It's a difficult choice.

It sounds decent enough for much gaming but might choke on the extreme interactive stuff. Personally, a little more muscle with the graphics would be my choice.