Given your needs in the OP, I'd recommend either a relatively lightweight regular ebike, or an electric folder.
A non-folding bike needs lifting up. Your existing bike weighs 19kg so I'd suggest you need to consider no heavier than that. Sub 20kg usually implies a non-removable battery due to reasons I outlined up thread. It typically means a fairly small battery too. However that's not necessarily an issue as range extender batteries are an option on many bikes.
A folder removes the need to lift the bike onto the racks, and also increases flexibility for getting on the train. It's luggage so you don't have to book a bike slot or risk one not being available. Electric folders do come with other compromises of course.
I'd carefully consider whether belt drive is worth the other compromises. Nothing wrong with it as a drivetrain, but it does reduce options. For example the Tenways bike you mentioned is a single speed. Given your use case of a day's riding with a few light hills that may be fine, but potentially reduces the kind of gradients you can get up. If you want gears with a belt drive you need a hub gear which means a mid motor, and quite a bit more expense. Going for chain drive gives more choice of bikes with more gears, for the price of a teeny bit more maintenance (i.e occasional use of a rag and a bottle of oil).
