How can I connect Mac Mini and Windows Laptop to one screen?

You’d usually want a KVM switch as a separate box, or (less likely) a monitor with an integrated KVM switch.

The KVM box or the monitor-integrated KVM will need matching connections for your particular hardware; probably miniDisplayPort or HDMI or Thunderbolt or whatever for video, and probably USB-A keyboard and mouse connections for that. Many (but far from all) monitors can have multiple video inputs. Fewer will have inputs for keyboard and mouse—Gigabyte, MSI, Samsung, and Dell do seem to have some KVM-integrated monitors on offer, though.

https://en.wikipedia.org/wiki/KVM_switch

I’ve had middling success with KVMs. Some have worked fine, and some get the display or the keyboard confused. Models from Raritan and Belkin have worked for some installs, though I’ve not installed a KVM in the past several years and available models will likely have changed.

If the Mac mini you are acquiring has an Intel processor and has enough storage, you can run both Windows and Mac on the Mac mini, either alternately using Boot Camp, or both together using a virtual machine; a hypervisor. Newer Macs including many of the current Mac mini models will have an Apple silicon processor and not an Intel processor, and with no way to purchase a supported version for that (yet?).

Or you can use an app on Windows such as the Microsoft RDP client to access the Mac “headless”. That will have a number of trade-offs, of course.

depend on the monitor too, i don't use any kvm or the likes my 27" asus monitor have 2 hdmi and 1 dvi and I can switch between them on a front panel button, i have my work laptop and my windows desktop and my mac mini connected to it and switch between them

Rudegar wrote:

depend on the monitor too, i don't use any kvm or the likes my 27" asus monitor have 2 hdmi and 1 dvi and I can switch between them on a front panel button, i have my work laptop and my windows desktop and my mac mini connected to it and switch between them

That works fine for switching the display alone, but not so well for sharing the same keyboard and mouse as was requested.

for that I use Logitech mouse of keyboard mouse and keyboard which support 3 different connection at once and support copy paste from one connected device to the other