The closest upgrade from the focal clear is pretty much the utopia in most regards, but that being said the clear is more neutral actually, as the utopia is even brighter so you have to make sure to later on get a good amp that reduces that excessive brightness at times lol, but it’s a very impressive headphone and a big technical step forward, still sounds decent on the rnhp, but that one is really picky for what it sounds good on, but it would still be a noticeable upgrade in technicalities from the clear even on the rnhp.
Another headphone that might be considered an upgrade with a signature that could share some similarities might actually be a diana phi, and while that sounds strange, it’s not a direct upgrade in terms of sound, it is something that someone who enjoys the clear might enjoy as it’s really technically capable and impressive, smaller but very holographic stage, and organic enough to sound convincing at the same time. This is pretty meh on the rnhp, I would personally suggest moving to an amp more sutable for planar for this one.
I do think that another headphone that could be worth looking into that might have some overlap for signature could perhaps be the audio technica adx5000, which while it isn’t as massive as an upgrade as the utopia or phi and could be a sidegrade in some aspects, it could potentially be appealing and a worthwhile upgrade for some. The 5000 is very very detailed in the treble and midrange, really organic with the right amp as well, it is really intimate but it’s very sharp in imaging and placement and is pretty dang capable with the right music. The bass on it does extend decently well but might lack impact and body for some, but generally it would take the more neutral bright sound of the clear and make it more suited and capable for more organic music genre (and actually works really well with the rnhp and bf2, but later on moving to a really natural tube amp is worthwhile).
There are a ton of other cans that are great but not direct upgrades to the clear, so it would really depend on what aspects you liked about the clear, and what aspects you would want to change. The reason I would say it’s hard to find more direct upgrades is mainly because focal is rather unique in how they handle dynamics and spatial recreation, focal cans are very dynamically alive and impressive in that regard, and generally the focal tend to make a smaller bubble of sound around your head instead of trying to lay it out in front of you, which makes it hard to find other headphones that carry similar traits so other upgrades outside of focal won’t be as direct.
If you really are just in love with the clear and it’s sound but not ready to make the jump to the utopia yet and want to maintain as much of the clear sound as you can, you could always just later on upgrade from the rnhp to something like a violectric v281 for something to make it a slight bit warmer and more spacious but keep it very controlled and detailed, or a headamp gsx mini for something that is more brighter clean but has good body, analytical without being harsh (although to me personally this a bit too bright of a combo), or perhaps something like a questyle cma800r for something neutral smooth but pretty organic sounding with the clear, or other options. This would give you a nice performance boost for the clear, and also make it easier to upgrade to higher end headphones later on without needing to get another amp (if you play your cards right)