Network problems as soon as I updated to 10.15.6

Did your MacBook start with Catalina? (Seems like it should have, being 2019.)

I'm simply wondering whether the "Legacy extension" could be pre-Catalina.

I also wonder whether the "Legacy extension" may have come with Google Chrome, or was added for Chrome.

Likewise, that "SSL Error" is especially likely to be tied to the issue: without a properly working Secure Sockets Layer (SSL), you will be, essentially, unable to "establish a secure connection."

Have you tried to perform a "recovery" of your system?

The fact that things work in "safe node", but not with "the normal booting", indicates that the problem is something that was added, at some time. (It can, also, be caused by missing or corrupt components, that are, temporarily, replaced by "known good" ones, by "safe mode".)

gabeneedsyourhelp:

Do you not see the problems, right there in the EtreCheck output, under Major Issues?

Take care of those! First Thing!

(By the way, I said nothing about any so-called "virus protection software".)

I see the following potential issues, Bradford Bosley, from your EtreCheck report:

Minor Issues:
These issues do not need immediate attention but they may indicate future problems or opportunities for improvement.
More than one antivirus app - This machine has multiple antivirus apps installed.
Heavy RAM usage - Apps are using a large amount of RAM.
Clean up - There are orphan files that could be removed.
Unsigned files - There are unsigned software files installed. Apple has said that unsigned software will not run by default in a future version of the operating system.
System modifications - There are a large number of system modifications running in the backgroud. Low performance - EtreCheck report took an unusually long time to run.
32-bit Apps - This machine has 32-bits apps will not work on current versions of the operating system. Kernel extensions present - This machine has kernel extensions that may not work in the future. Sharing enabled - This machine has sharing services enabled that could be a security risk.

Additionally, we have the following, which may be an issue:

Antivirus software: Apple, Avast, and Malwarebytes

"Malwarebytes" in a known culprit with many issues.

I have seen issues reported for "Avast", recently, as well.

There may be additional issues hiding in the "unsigned software", "system modifications", and/or "kernel extensions".

I'm having the same problems. Here is my Etrecheck report

I'm simply glad everything seems to be OK, now, gabeneedsyourhelp.

However, may I strongly recommend you rerun EtreCheck, to make sure that, at least, the Major Issues are corrected?