While there are a few leftover elements from the DSLR era, really the concentration of new cameras and lenses is in the area of MILCs - Mirrorless Interchangeable Lens Cameras: specifically the R series of camera bodies.
These generally represent a significant change in technology and some major improvements in performance.
For your situation, I would recommend a good quality full-frame R body of which there are a few choices. The features of the better cameras in this series include fast focus and tracking for eyes and faces of animals and humans. The better FF bodies: R3, R5 and R6 also have In Body Image Stabilization (IBIS) that helps control movement of the camera, and with most R-series lenses is combined with the Optical Image Stabilization that is a traditional hallmark of L series lenses.
You should be able to reliably use your L-series lenses with the new R-series bodies, but if you want to maximize the performance of the new technologies, you might want to eventually consider some RF lenses - the L series lenses are brilliant, but pricey.
If you look at the numbering hierarchy of the DSLR series the new R-series is, to a degree, echoing that, certainly for the top levels:
DSLR ...... R-Series .... Comment
1D R1 Yet to be announced uber Flagship
R3 Flagship Sports and events camera, initial version current
5D R5 Best all-round pro level camera. Initial version current
6DII R6II Brilliant value camera at lower price point, 24MP sensor, IBIS etc.
The R1 is expected to be the flagship MILC model, but with no R-series unit specs firmly announced, comparison of those is speculative at this stage. However it is likely that the R1 and R5MkII will be announced in the next quarter or so.
The R5 is the current flagship general purpose FF sensor camera. In these days of frenetic development of the R range, is getting relatively long in the tooth, so while it has a 45MP sensor, it is not stacked, but has a spread of features for a much wider range of applications than the R3. It has the more conventional build, using the higher capacity LP-E6NH batteries and can take a BGR10 battery grip to provide balance, more energy reserve and the dual portrait controls.
You can compare the specs for the 1D, 5D and the R3 and R5 HERE . The R5 has undergone multiple firmware updates since its release to fix initial bugs and to improve performance. You can get a cumulative list of those by looking at the R5 firmware update description page.
Depending on your budget, you might want to consider the EOS R6MkII. This has a 24MP sensor, great tracking and focusing, and is significantly cheaper than the R3 and R5. It is slightly better in low light situations than the R5 and might be a good candidate since your 5DII will have a sensor capacity lower than the 24MP of this unit. I have the R5, R6 and R6II models and use the latter two more than the big sensor unit. If you don't need 45MP, then you can save money and possibly look at some RF glass.
So, much depends on what PRECISELY you want from the camera itself. Compared to the camera you are coming from, which is quite old, ANY of these units is a huge step forward.
As regards your lenses. As you have Canon L lenses for the DSLR body, then you should be able to adapt them fine via the Canon EF-RF adapter and they should do so OK. If you have 3rd party lenses, you need to make sure that they will work as expected - Canon makes absolutely no warranty that lenses made by other manufacturers will work on their cameras. They want to make sure that everything in a developing platform works well, and (like Nikon) will authorize makers to create R-series lenses on a case-by-case basis.
cheers, TREVOR
The mark of good photographer is less what they hold in their hand, it's more what they hold in their head;
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
