Sounds like a permissions issue.  Log in as Admin to see if it works okay.

I am logged in as the ADMIN user, not that!

They are still in the finder. On upgrade you lose customisations.

Finder / Settings / Columns. Scroll down on the left column to see the optional fields.  Include them in the Selected Fields showing on the left.
Do this for each user.

I've done that and that is the issue. They aren't available on the left to select?

FYI, this is bug an has been confirmed by Sage Support. It isn't working in 2022 either. It broke somewhere between 2017 and 2021. I'm waiting to see when there will be a fix.

Another update. Sage has found it is not a bug. Here's the fix:

"Please see the attached KB article to enable optional fields in lot finder.  Updating the IC.INI file will enable optional fields."

To enable serial/lot optional fields to the serial/lot finder, you only need to add the following lines to IC.INI, under [OptFldFinderBindings] section.

[OptFldFinderBindings]
IC0830=IC0832,IC0377[13]
IC0810=IC0812,IC0377[14]

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