Can I use my iMac as a monitor for my MacBook Pro?

Based on your MBP's description, no. Target Display Mode has been dead for over 10 years (2014). Please remember iMacs are computers, they are not external displays for other devices. If you want/need an external display for your MBP, please buy one. You can find them as low as <$100 or as much as $1500, however you can find a nice one in the $300 range. If you decide you want to get one, just think about what you really want including:

• display size
• resolution
• feature set (hub, ports, speakers, camera, etc...)
• type of connection
• price point

Once you have thought about those things then your search becomes much easier as there are many many external displays available.

From the screen size (14"), I'm pretty sure that is a MacBook Pro with an Apple Silicon (M-series) processor. If it is, your MacBook Pro does not support using any iMac as a Target Display.

Even if that was not an issue, none of the 27" iMacs with 5K Retina screens support Target Display Mode. The feature went away when the first 27" 5K Retina iMac came out.

See if your Macs meet the criteria.

Use your iMac as a display with target display mode - Apple Support

Using an iMac as a monitor - Apple Community