can i upgrade my 21.5 imac 2019?

Install memory in an iMac - Apple Support

“Memory is not removable by users on the iMac (Retina 4K, 21.5-inch, 2019). If you’d like to upgrade the memory in this model, an Apple Authorized Service Provider can help. Before you schedule an appointment, confirm that the specific Apple Authorized Service Provider offers memory upgrade services.”

I can not see why, you not can upgrade,your 21.5 iMac 2019?

Because Apple has said so here:

https://www.apple.com/legal/warranty/products/embedded-mac-warranty-us.html

This Warranty does not apply

(f) to damage caused by service (including upgrades and expansions) performed by anyone who is not a representative of Apple or an Apple Authorized Service Provider (“AASP”);

Why not?

Difficult,or not?

I can not see why, you not can upgrade,your 21.5 iMac 2019?

OWC,is not the very cheapest,on the internet marked?

Yes! Ram,to IMac,or Macbook,can be very tricky,but give it a try?

Make, an, Google searcing,on this issue?

The 21.5" models are not considered user upgradable; therefore, you will void any warranty you may have on it unless it is done by an authorized service provider. If it is beyond the warranty, go for it, but it is not easy. And, OWC does not even list the 2019 models in their install videos:

https://eshop.macsales.com/installvideos/

All that’s being said is the 21.5 iMacs do not have easy access for user installed RAM. You have to disassemble the machine to do it and that’s not for the typical user. One wrong move and your machine is toast. If you are the tinkering type then sure, go right ahead but your warranty will be invalid. If you screw it up you will not be able to take to Apple and ask them to fix it. They won’t touch it.

Yes. Visit OWC for compatible memory and installation instructions.

Actually it is as Kappy stated. It's just difficult.