Using new iMac as an external monitor for a Lenovo ThinkPad (work laptop)?

I'm thinking of buying a new iMac (unsure re model but probably the 4K one) as a desktop computer for home (my MPB is probably eight years old and on its last legs!)

Given COVID-19 I'm now working from home via a Lenovo Ultrabook ThinkPad and my neck is killing me.

I'm wondering if I'm potentially able to use the new iMac as an external monitor for my work laptop? If yes, what cords and whatnot would I need?

Please speak to me as you would a small child - my IT knowledge is very basic... Thank you in advance of your help.