OneDrive slower than dialup speeds in syncing

[c_pm99]

I have checked onedrive settings, and set it to "do not limit" speeds.

Yet, I've been uploading a 12 mb file for 10 minutes and it's only half done.

I've been on a video call during this, so clearly my upload speeds are up at at least 1000Kb/s, yet, the sync is reading 26 KB/s.

After getting off the video call, it remains slow, so that's not the issue. Nothing else is transferring as onedrive moves like molasses.

Meantime, I'm only doing this because emailing a 12MB attachment fails without a warning (via Outlook for desktop).  I've been trying that for 20 hours now, repetitively. One time, I got a message of "could not upload attachment, please try again", but every other time not even an error message to let me know it failed.

This is a professional Office365 business account, and Microsoft's system is anything but Professional.  I'm just trying to email or send a simple 12MB attachment, but with either 1995 era speeds, or zero error messages, this is completely ridiculous.

What is going on here?

[#2]

@c_pm99 Since we know nothing about your setup, operating system, network or other factors: try the troubleshooter steps: https://support.microsoft.com/en-ie/help/4028268/windows-10-fix-onedrive-sync-issues

[#3]

@Mike Williams  The link you sent just says to check if windows is up to date, and onedrive is running, which it clearly was.

I am on a 2020-bought Thinkpad with up-to-date Windows 10.  I don't know any situation at all where dialup speeds would be ok.  No one is on dial up anymore, and I'd written that I'd checked my network, which was high speed both up and down.  Other services worked fine with no issues.

Today, the same file that was taking forever to upload, did so in 2 seconds, which is what is normally expected.

What real options does a user of Office365 have to figure out why Microsoft's network is taking a dive?  The link given as a response definitely does not cover this real life situation.