When Ray Tracing is supported by the GPU, the game runs with decreased performance even when Ray Tracing is not enabled in the settings.

From testing, an RTX 3080 Ti gets drastically lower framerates than a GTX 1060 does in the same world with the same settings. In situations that are known to cause frame drops (such as having a large number of entities, lots of item frames, or using a high-res resource pack), the performance hit is greatly exaggerated on RTX GPUs.

It can be proven that this is not an issue with the GPU itself by using the workaround listed below or downgrading the Nvidia drivers to an older version (442.74) where Minecraft doesn't detect the GPU as Ray Tracing capable. The performance will be back to expected levels. Some Windows versions may also stop the game detecting RTX, fixing the performance. Versions without Render Dragon (meaning they don't have RTX support) also have correct performance.
It seems that when the game does not detect a Ray Tracing compatible GPU, it runs at the FPS it should.

Minecraft Preview shows that RTX cards use "D3D12 RTX" and GTX ones just use "D3D12". The RTX version has a large FPS hit for players who aren't using Ray Tracing.

Steps to test the difference:

1. While using a GTX GPU that has no ray tracing capability, get into a situation that will tax the system slightly. (for example place 100 filled item frames or spawn 50 mobs)
2. Make sure VSync is disabled and note the average framerate.
3. Swap the GTX GPU for a more powerful RTX one. (or disable DXR Raytracing in NVIDIA Profile Inspector)
4. Load the same world with the same graphics settings. (with Ray Tracing off in the settings)
5. Experience a lower framerate than the less powerful GPU.

Expected Result:
The RTX graphics card is significantly more powerful than the GTX one, so it should have a higher FPS.

Observed result:
The RTX graphics card performs much worse than the GTX one. 

Screenshots/Videos:
Performance comparison between GTX 1060 and RTX 3080 Ti, with all other hardware/settings/packs left the same.

Notes:
When Ray Tracing is disabled in the game settings, it is not fully disabled. Something seems to change when RTX is available for the GPU.
This bug looks to be the root cause of MCPE-153297, MCPE-111547, MCPE-157142, and possibly MCPE-142934 for some users.
I think this bug is capping the performance of everyone playing using an RTX GPU, but goes unnoticed as people with frame drops aren’t comparing the performance to a lower-spec GPU without Ray Tracing support.

Workaround:
With the latest version of NVIDIA Profile Inspector, you can now disable DXR Ray Tracing for only Minecraft, fixing performance! Select the Minecraft profile and set "Raytracing - (DXR) Enabled" to "RT Disabled".

The game will report that your device is incompatible with RTX, however you'll now have performance that matches a non-RTX GPU! If you ever want to use Ray Tracing, just change the setting back to "Default" and the in-game option will be unlocked. For some reason the Minecraft profile in Nvidia Profile Inspector doesn't affect Minecraft Preview, so to test D3D12 on that version of the game you'll need to temporarily disable DXR on the global profile and re-enable it when you're done.

Alternate workaround:
Minecraft switches to D3D11 if the GPU recovers from a crash while RTX is enabled.

We can test a "timeout detection and recovery" by running "dxcap -forcetdr" in an administrator command prompt. This may require "Graphics Tools" to be installed in the optional features page of the PC's settings. When I tried this the screen went black for a few seconds and then Minecraft Preview reported that it was using D3D11 instead of D3D12 RTX! There's a black screen in game until Ray Tracing is off again but after that it'll be on D3D11 until the game is restarted. FPS improved by a lot around item frames and 512x packs worked perfectly. Doing this can and did cause issues with other software/hardware. I'm not an expert, so if you use this it's at your own risk!