This was asked on a Facebook Group and I felt like a comment wouldn't suffice.

I've had to have a macOS workstation available for a long time. Sometimes even multiple macOS versions. So I've been through a bunch of setups, I've listed them all below.

Currently I'm rocking a Mac Mini with an upgraded SSD sitting in my basement in my my quater rack with my Synology SAN. I use TeamViewer and VNC to manage it.

You can grab an older Mac Mini with an HDD and it'll be super slow ;) But will do the trick.

You could also install an SSD into the Mac Mini if you have one that is serviceable. Look up your model and then "install ssd" on Google and you'll either find instructions or potential a kit.

Currently I'm rocking a Mac Mini with an upgraded SSD sitting in my basement in a quarter rack wall mounted with my Synology NAS. I use TeamViewer and VNC to manage it.

If you don't want to take apart the your Mac Mini or maybe you have a spare laptop kicking around. You can always boot an Mac from USB or USB-C. This works really well and I personally use it for repairing macOS sometimes when the main volume has issues or runs out of space.

You could also run a Hackintosh https://hackintosh.com if you have a PC kicking around that supports running the Hackintosh build.

Lastly you can run a virtual instance of macOS on Proxmox or KVM. This can be done on PC hardware. I use the Lenovo M720q Tiny, you can buy them off eBay.

These are great for running Proxmox and deploying Windows and Linux VM's for testing.

Here's the Proxmox Article https://www.nicksherlock.com/2020/04/installing-macos-catalina-on-proxmox-with-opencore/

Here's the KVM Projects

Once you get your solution in place. You don't have to use a monitor, keyboard and mouse. You can use either Teamviewer or VNC. You can even use the Proxmox viewer! Here's link to some common remote access software.