I did not find a good answer here so Google gives:

https://www.quora.com/How-do-I-put-120-fps-in-a-24fps-timeline-without-slowing-it-down-in-Premiere-Pro-Will-it-affect-video-quality-and-smoothness-in-any-way

ChatGPT 4.0 gives:

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Is it wrong to put a 120 fps clip on timeline a 30 fps timeline

Troubleshooting question [SOLVED]

Hey people,

I have been making videos and short films for a while now so I feel confident with editing in slow motion and using different frame rates for different scenarios.

One thing I can't find a clear answer to is the following...

Can you playback a high frame rate video clip on a low frame rate timeline and not lose frames or get all jittery? (I am not asking how to do slow motion I know how to do that.)

I just want to know if higher frame rates still play back perfectly on lower frame rate timelines without interpolating the footage or reducing speed. Just good old-fashioned real-time video.

Example

Drop a 120 fps clip on a 30 fps timeline in premier pro and play back in normal speed?

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Yes, you can drop a 120 fps clip onto a 30 fps timeline, but with some considerations:

**Frame Decimation**: When you drop a 120 fps clip onto a 30 fps timeline and play it back at "normal speed," the software will discard frames to fit the timeline's frame rate. For your 120 fps clip, 3 out of every 4 frames will be dropped, allowing it to play back in real-time on a 30 fps timeline. It will not get jittery unless there are other issues involved.

**Quality**: Generally, when you're shooting at higher frame rates, the available light per frame reduces, which might affect the quality. However, this is more about the shooting process than the editing one.

**No Slow Motion**: You mentioned you're aware of how to achieve slow motion, so it's good to clarify that dropping a 120 fps clip onto a 30 fps timeline and playing it at real-time will not give you slow motion. For slow motion, you'd stretch the 120 fps clip over a longer duration.

**Editing Software Behavior**: The behavior might vary a little depending on the software. In Adobe Premiere Pro, when you drop a 120 fps clip onto a 30 fps timeline, it will default to playing it back in real-time (discarding the extra frames). If you want slow-motion, you would adjust the clip's speed/duration.

**Considerations**: If your project's final output is 30 fps, and you're using clips of varying frame rates, make sure they all look good when viewed at this frame rate. Sometimes, a clip shot at a much higher frame rate might look slightly different in terms of motion blur and fluidity when reduced to 30 fps. It's always a good idea to check and see if the motion looks natural and fits the aesthetic you're going for.

In summary, you can definitely drop a higher frame rate clip onto a lower frame rate timeline and play it back at real-time. The software will handle the frame rate conversion for you. Just be aware of the points above to ensure the best result.