You should be able to use both the UHD Graphics HDMI and VGA ports at the same time and run the monitors as independent screens. But VGA is a low quality analog signal, so you may not be happy with its performance, assuming one of your monitors supports VGA. You have a PCI-e x16 port on the motherboard for a full-height add-in video card. The main issue here is the size of your PSU, which will limit your choice of video cards. The stock PSU is either 260W or 360W. There's a table of video cards that Dell offered with this model on page 19, here and others may work too. You don't have to buy a video card from Dell, but "retail" versions of the same card may have different PSU requirements, and different ports so make sure you check that for whichever retail card you want and confirm that the length of the card fits into the case too. Most add-in video cards only have one HDMI port and one DP and/or one DVI port. So if your 2nd monitor doesn't natively support one of those ports, there are adapters like DP(PC)>HDMI(monitor) that will work, as long as you make sure it has the right direction, because they typically only work in one direction. Or you could use HDMI on the video card for monitor #1 and the UHD HDMI port for monitor #2. A third option would be to buy a USB3>video dongle with a port supported by monitor #2, eg USB3>HDMI. Just make sure the dongle support your version of Windows and the "native" (= "recommended") resolution of the monitor you connect to the dongle.
I've been searching for an answer for hours  to the question of adding a second, non carbon copy version, monitor to my single HDMI port Inspiron 3891.  This is the Dell Inspiron Desktop - 11th Gen Intel Core i5-11400.  Model i3891-5012BLK-PUS w/ integrated Intel® UHD 730 Graphics.   Of course using an HDMI splitter didn't work and nobody else in the Internet Universe appears to want to operate dual independent displays.  If so, they aren't asking for help online.  I'm wondering if it is possible to install a different graphics card with dual HDMI ports or even somehow utilizing the VGA port along with the existing HDMI slot?  And if I could pop in a different graphics card I'd appreciate recommendations.  I've done it before but on much larger Motherboards.
Dual Independent Monitors on Dell Inspiron 3891 (Costco bestseller)