An old desktop MAC--how can I make use of it?

What kinds of connectors does the monitor have?

Knowing apple, it is a mac proprietary connector and no industry standard ports for other uses.

If you by some miracle have an hdmi port, you could probably put a google firestick in and cast to it from your laptop, or connect directly via the hdmi cable if your laptop has one.

If your monitor uses a thunderbolt adapter, you can use an adapter to convert that to hdmi, which all modern laptops should support.

Here is one example:

https://www.amazon.com/AmazonBasics-Mini-DisplayPort-Thunderbolt-Adapter/dp/B00NH13K8S

It will of course depend on the actual adapter port(s) on your monitor, but you should be able to connect it to a modern laptop.

I have my old iTunes library running from a Mac mini in my basement. I shared the library with the PC in my living room. It's pretty cool.

On my clock radio from the same era. Love waking up to Adele.

you might need to need to buy some cords.

Post the links of the pages you were looking at please.

Just kidding. I have the exact same situation - 2010 iMac that still runs, but is way outdated and can't really be updated. But it's got 10 years+ worth of family photos and videos on it. They're backed up on Time Machine AFAIK. Probably going to buy a new one and hope that the nice folks at the Apple store can port everything from the old one over to the new one.

Likewise, I am on a newer (2015ish) MacBook, but I have no idea if you can connect the two.

depending on how new the laptop is, you probably just have 4 identical USB-C ports. You'll need a cable with USB-C on one end, and HDMI on the other. Easy to find on Amazon, etc. Good luck!

Before ordering any cables, read up and make sure it'll work. Here's a good article:

https://www.chriswrites.com/how-to-setup-your-old-imac-as-a-display-monitor/

You can use the 'About This Mac' menu item to see exactly which model of iMac you've got. 2009 and 2010 iMacs had "mini display port" connections and Thunderbolt showed up starting in 2011 models.

It's tough to figure out because Apple has used a bazillion different video cables over the years, but start with figuring out exactly what models of iMac/Mac you've got and lookup the display connector types.

I'm guessing you just need a mini-display port cable, unlikely to find it retail but easy enough on the web. Good luck!

I have a bunch of cables that I've used to connect to all sorts of things over the years so I'll play around and see where Amazon (or better) can fill in the blanks. Or maybe just use it to broadcast youtube exercise videos, since it's big enough for me to see them--unlike the laptop!

replace the HD with an SSD, kick up the RAM to 8 or 16, update OS to High Sierra, and that thing will still work great. I've got an old Mid-2011 with those updates and it kicks ass. Just about as fast as some of the new ones. You won't get the latest security updates, but in almost 25 years running Macs I've never had a problem when running older OS versions w/o the latest updates.

Adding memory could be really easy depending on the model
https://www.lifewire.com/imac-upgrade-guide-2260872

And more complex options over on iFixit, eg. replacing the disk with SSD:
https://www.ifixit.com/Store/Mac/iMac-Intel/SSD_Upgrade_Kits

I've got some really old systems still running just fine

I use this to 'mirror' my iMac screen on a 37" 1080p TV.

Works great and email is sooo easy to read!

Videos are great, Amazon Prime, Hulu etc will all let you watch on a regular tv with good stereo audio.

Get the cable...
https://www.apple.com/shop/product/HHLY2ZM/B/belkin-4k-mini-displayport-to-hdmi-cable-2-m-65-ft?fnode=29babd189b1aa943381df02bbfcf70840b5c961a17122fac1ac786d24c020972b527f6749155f6b1cb21cd7d90147ea6bf7963cc66240b8fd0fc55b17ebcae9c079db01b2c7975a7f009ee63451de5801f1139a694fd841ac3c8c551942c074c12db79505fa0a7a3eec1c6249f7f3403&fs=f%3Dcable%26fh%3D459d%252B45c4

Change your System Prefs>Display to make sure the 'mirror' option is selected. Must have the cable plugged in to see this option.