Is this really how the standard online form of a custom record looks like? I was expecting that it will look very similar to the UI version.

Yea that’s it You can do some formatting in appearance but that only changes colors and logos If you know HTML you can put custom code in there to make it nicer

Thanks again, @MGBC. I'm just wondering if you are aware if it's possible to set the value of a multi-select field from an entity record to a transaction. It gets executed but the logs say it is set to "()" which is null in the UI.

Yes from this documentation it does seem possible. It talks about multi select at the bottom https://docs.oracle.com/en/cloud/saas/netsuite/ns-online-help/section_N2751166.html

Thank you!