Can I use two 2010 iMacs as displays for M4 Mac mini?

None of the options in the 9to5Mac article are workable with any iMac as the primary monitor for an M-series Mac. Carefully note this advisory posted on the support home page for Luna display:

The red emphasis is Luna's, not mine.

The short answer is a resounding no because your M4 MM is too new. Please carefully read Target Display Mode and it will explain what combinations you can use. In your case the Mac mini is the reason it will not work, it simply is not supported.

If you want/need 2 displays for a MM M4 then you need to buy them, it's that simple.

Those iMacs support Target Display Mode using Mini DisplayPort input, but Apple added restrictions such that current Macs do not support using any iMac as a Target Display.

not as the only monitors you need a real monitor too

and the performance of such setup in terms of visual delays is not suppose to be a pleasant experience

also the two macs will use a lot! more current than a normal monitor so it will cost more on the electric bill

the old target display has been dead for a long time

try reading

Use iMac as monitor: 5 Solutions - 9to5Mac

It might be worth using Luna Display to be able to use a 27" 5K Retina iMac as a second display – even given the limitations. Apple wants $1600 for a 27" 5K Studio Display, and even now that we are starting to see a few third-party 27" 5K displays, you'd probably pay at least $800 – $950 street price for one of the less expensive ones.

Given the price of 27" 2560x1440 and 27" 3840x2160 displays, I don't believe it's worth a lot of money to try to reuse a 27" 2010 iMac's 2560x1440 pixel display. The money you would spend to buy a Luna Display device (or rent DuetDisplay for as long as you wanted to use the screens of those old iMacs) would be better put towards a standalone hardware monitor.

It's not like in Late 2009 – when a standalone 27" 2560x1440 display from Dell went for $1200 ($1000 on sale). Then, the DisplayPort input feature of the 27" Late 2009 iMacs was a definite point in their favor.

I can assure you, without reservation, that you will NOT be satisfied with the suggestions presented here to use those iMacs, not even one, as displays on a M4 Mac Mini. Take the majority’s advice and buy two monitors.

Not even one. Using an iMac as a monitor - Apple Community explains.