Post Upgrade (it seems) poor wired & w/less internet connectivity &...

Here's a description of my problem, I'm hoping someone can shed some light on:

My Dell laptop, running Win 10 Home got very slow about six weeks ago and the audio was 'crackly'.
It was fixed after uninstalling a couple of updates. (I don't remember which)
About 2 weeks ago it began again; but now both WiFi and Wired connections were very slow - only managing between 3 - 8 Mbps over a 60 Mbps connection.
This time there were no recent updates shown that could be uninstalled AND and in Updates it said my build was upgraded and so there were no earlier restore points. (not sue if I'm explaining that correctly)
I then checked for new updates and installed them. That didn't work so I uninstalled them.
I then noticed that while my network speed was dead slow in "Normal Mode" it drastically increased (40 Mb/s) in "Safe Mode with Networking".
Anyway.... to speed things along (because the exact details escape me) I tried:
- installing and re-installing updates,
- system restore and a reset - both of which failed.
I reached a point where I couldn't go back and my network connection was slow in both "Normal and Safe Modes" and some App shortcuts (MS News couldn't be launched from Notifications) were broken.
So I manually upgraded from 1809 to 1909 - no fix; same issues.
Uninstalled my anti-virus (Bitdefender) - nil fix.
Was able to roll back to 1809 and stuck here now with same issues.....