Ideas for attaching table top to legs

Dado or grooved definitely the way to go. I see a lot of tables with metal flat or metal U track and inserts that screw into the tabletop and the legs slide into the U as a groove and are screwed from the sides. This is common on the river tables. It's metal but understand on rivers tables- people seem to not trust the pours I guess and they spend so much time on the top to have time to make the legs pop.

You have a wooden top solid or laminated so I would not go plate or metal. I would go old-school attachment. I would stop rout a groove that is large enough for both the legs a 1in wide 2 inches deep. I would screw and glue the block in and used three bolts through the 2 into inserts in the legs. This would be inside of the legs so you do not see from the outside look. The block would be up and out of sight. I would also add some pegs where the base attaches to the table glue into the legs and mortise the table to receive them it will help assembly for installation. If you did not plan extra length on the legs I would have small ebony feet. Can't go wrong with the hardness and support. It will still give the same look and you will not see the supports at top or ebony at feet.

I put threaded inserts (brass) into the underside of the top, I then bolted the legs to the top from underneath.

You can see the holes. I elongated them so the top can expand or contract with humidity.

I think I got the threaded inserts from WoodCraft. They take a 1/4 20 bolt. You can lift the top and the legs are not going anyplace.

If you go to my project page you can see the threaded inserts before I drilled the holes and screwed them inplace.

I would just run some flat bars across the top sunk in flush.
I think the flat bar would be easier to find at a big box store compared to a metal plate.

" it seems like the solution you first describe with U-profiled metal tracks is the same solution bamdit571 described?" It is However It is not flat as first described or Leroy shows since you are depending on the screws to hold the leg. I was talking types of steel channel (C Purlin) add short inward-facing lips to the end of the extensions. The sides are longer than what I have seen inserted into the table to keep the live edge from warping. You route a groove into the table and use inserts to secure it. The Channel sides are drilled through for bolts through the legs. This gives both torque strength and up and down securing. Best pict I found on channel. simple if you want to just use some steel or aluminum. Pict of type of channel.

Old school is how Trestle and picnic tables in medieval England were secured.(They used mostly sliding dovetails to secure a brace or cleat to secure through-bolts or dowels through.) In tables in the 30s legs were also attached this way for Dinning and kitchen tables. You basically have a trestle table with good surface support, but no side or torque support. The pict was an easy way to describe, obviously, the brace need not be that depth. 2 in max. This was done in many ways called a cleat but the best is a sliding dovetail (although might not work with your design as would show on sides). The leg is bolted through the table brace cleat. All these are no metal added all wood material except the assembly bolts.

There are a few ways from simple to more complex.
Simple
or

These are small cleats but also more complex to the bottom image in this link here but it is certainly secure. https://www.props.eric-hart.com/wp-content/uploads/2012/03/construction-of-a-table.png.

It is simply a glued brace to drill holes through. The groove helps to counter-movement. You really only need one on the inside of the legs. This would not change the look of your design at all and the braces would be out of sight from view except for the wood workers who climb under to see how things are built.

The last part was inserting dowels or pegs just to index the table. Like this pic. This just helps to easily put the table together, as that is a large top, and would not want its legs to slide out accidentally and the top to fall on the guy assembling it.

Should have just drawn a picture of what I meant, but not very good at drawing. I learned for next time, as this may not be clear to the simplicity of the method I described.