I used this forum to determine the best value RAM upgrade which seemed to be from Crucial - upgraded to 8GM RAM which has improved the performance to a much more acceptable level. Interestingly the entry level 3891 is now 8GB and 4 core!! Says it all! 
We have acquired 3 new Inspiron 3891 PC's for our office to replace a 14 year old PC and all 3 are slower than the original! All we are  running is Office 365 using Word and Excel and the internet and apps are taking 45-60 seconds to open, the internet takes for ever to scroll and Outlook is yawningly slow to open messages. We've tried all the upgrades and Windows 11 without effect We're tearing our hair out especially as Dell Customer Care is a joke. We contacted support and spoke with someone somewhere in the world with a bad line and heavy accent which made explaining and listening to the problem difficult. They did help diagnose the hardware which was OK and suggested contacting software support. Even though we were still under warranty I couldn't believe we had to pay £48 and was told we would have to claim back through Warranty. The person I spoke to was helpful (again somewhere in the world) and gave me  instructions to reload Windows and make contact if there was a problem - there was a problem but I couldn't get in contact with the assistant - only to receive an email that Dell were glad it was resolved - NO IT WASN'T! and despite numerous emails to this effect I've have had no response. I notice the issue raised in the forum a few times and the suggestion that disabling hardware acceleration in Edge should help but this has not made any difference! It sems impossible to talk to anyone in Dell to be able to say please take these PC's away! If anyone has any ideas I'm on my knees for help!!!  
INSPIRON 3891 RUNNING SLOW - RUBBISH!