If I want to implement custom code in the entity's Save() method (in SelfServicing using LLBLGen Runtime Framework) I would think I could do it like so:

public partial class SiteEntity
    {
        public override bool Save()
        {
            if (this.IsNew)
                this.CreateDate = DateTime.Now;
            this.LastUpdateDate = DateTime.Now;
            return base.Save();
        }
    }

However, this code will not compile due to 'SiteEntity.Save()' cannot override inherited member 'EntityBase.Save()' because it is not marked virtual, abstract, or override

I am targeting .Net Standard if that makes any difference and I am using LLBLGen 5.4.2 with the hotfix applied.

Is this no longer the right way to do this?

Override InsertEntity() and UpdateEntity() (set the values you want, then call the base method)

That was it exactly. Thank you and sorry if this was in the docs and I missed it.

This is now deprecated... what should I use in it's place?

Are you talking about UpdateEntity method?

Quoting the docs: The following breaking changes have been in LLBLGen Pro Runtime Framework v5.6.

(SelfServicing) EntityBase.UpdateEntity() is now marked as obsolete with error severity, as the method is never called/used. You should override EntityBase.UpdateEntity(IPredicate) instead.

Ref: https://www.llblgen.com/Documentation/5.6/LLBLGen%20Pro%20RTF/migratingcode.htm