iMac 13.1 27" 2010 Highest possible Hardware and OS upgrades

[Fcis]

I have an iMac 13.1 27" 2010 and I wonder what is the highest possible hardware upgrades (GPU, Memory, CPU,....)? and also what is the highest macOS? like is there a possibility to get macOS Mojave installed on my iMac and have things still functioning, such as Airdrop, and other things? Also ?

 

[USB3foriMac]

You still have "Macintosh HD" as a startup drive, which probably means that you are not using a SSD. To replace the spinning HDD with an SSD would be the most efficient upgrade you can do.
Next, you can search for the graphic card update thread (top of the list), the USB3 upgrade options, and Bluetooth/WiFi upgrade.
As the 2011 model is a lot more upgradeable, you could also buy a spoilt 2011 for nearly nothing, and replace the spoilt parts with those from your machine. While doing that, add an SSD.