Sure, when you say "my computer" I'm going to take that less than literally. I hope you have a spare one to do this with because you'll want to modify it somewhat to suit that purpose.

First, you'll want to install a secure operating system, a form of Linux like Ubuntu is a good start.

Second, you'll want to load the various software you'll need to do transaction signing. There are online tools that you can download and save as files on your desktop so that you can verify transactions and check signatures. Coinb.in is one that comes to mind. It might also be nice to have a QR code generator and a QR code reader to make it easy to transfer data without a network connection.

You can probably use Electrum offline to generate keys and addresses like a HW wallet would do for you.

Third, keep this computer offline. Unplug the ethernet cable and remove the wifi card. Disable bluetooth or remove that if it's a card. You don't want the computer communicating any other way than via the camera and qr codes and perhaps thumb drives.

To actually make a transaction you'll have an online part where you check and choose available utxos and put where the coins are going. Make sure not to donate a massive fee to the miners! Then the offline part would happen by sending this unsigned transaction to this specially prepared computer, verify the details, sign it, then share it back with an online computer or phone to broadcast it.

For privacy you may want to do the online parts over Tor. Someone wrote up a more in-depth protocol for this called the Glacier protocol and you should probably use that. What I write above is more like general guidance on what's required to use your computer as a hardware wallet.

What is actually a hardware wallet? A signing device. But that hardware wallet also is a cold wallet, a wallet that is not supposed to be used as daily wallet. You setup, save the xpub (for future deposits) and then hide it in a safe place and not open it anymore, only in an emergency situation. For checking the balance or depositing, YOU DO NOT NEED TO OPEN IT or put it online.

Please read these guides:

Use the 3 levels of stash: hodl, cache, spending

Respect