@aeva You may well find that the cost of trying to upgrade your old machine is higher than buying a new one, especially if you are running Windoz and are getting hit with the Windoz 11 issues.
(If your machine only has VGA/DVI then it is quite old.)
Remember, the Display Port over USB-C is DisplayPort - and a lot of monitors do not have USB-C (with Display port carriage) or even native display port.
(I tend to run Linux so I am only mentioning the Windoz issues second hand.)
I've been quite pleased with the NUC and similar small sized mini-PCs. (I"m using ASUS, Moginsok, and Geekom ones, but they can be a bit pricey.)
Also DP-over USB-C tends to require good quality cables - cheap USB-C cables may not work.