Thanks for the info.  I don't know if you saw it, but there's 3 different sets of instructions for updating to the 19/7/2019 A25 BIOS if you scroll down:  [URL]  I have no idea what, if any, differences there are between the two A25 BIOS' because I couldn't find the 30/5/2019 version.  Double checked using Dell-Australia and couldn't find.  I'm thinking there's a very chance it can be left. A few Win10 security tips: 1.  I found Ransomware protection off by default.  But at least it stays on thru the updates. 2.  I didn't think to check when updating to 1809, but checked once it got to 20H2.  System Protection was off for both drives (SSD + HDD) and Data Execution Prevention.  On a side note, one of those 2 could be the reason, I think more likely the latter, I have to turn off Windows Defender to scan from my Canon TR4522 printer.
I use the 'Dell Support Assist'. I've just purchased a 2nd hand  Optiplex9020 and the support assist has suggested the  urgent update of system bios Version A25 dated 30/5/2019 to a release, dated 19/7/2019. (update package for windows,  file name O902OA25.exe) I keyed  OK, ' support assist' went thru the motions and asked for  "restart"  to complete .I keyed OK and  ended up with a 'frozen blank screen' I had to turn of/unplugged power cord to enable a recommence. The update did not occur , system page still shows  version A25 19/7/2019. My question to anyone who can is,  Do I need this ?? if so , how to overcome the restart hiccup. thank you in advance,  JohnPeak.
Optiplex 9020 System BIOS