[HELP] Removing chroma rainbowing

[Selur]

I have tried several upscale options, should this be done at the same time as the chroma de-noise, or as a separate step?

I would do all the steps you mentioned (including the deinterlacing) in one script and not create an intermediate file, especially when not using a lossless format to same the intermediate steps in.
But depending on your system and general workflow doing each filtering separately with intermediate files is also okay, as long as lossless formats are used.

About the resizing:
a. before thinking about upscaling I would look into cleaning the clip up a bit by adding MCDegrainSharp, TemporalDegrain or SMDegrain after HQDering and some deblocking (Delock_QED) before it and may be even add some denoising after the degraun.
b. since the clip hasn't much details to begin with using an ml based resizer like RealESRGAN, SRMD, RealSR and similar will probably lead to more trouble than it is worth (assuming you are not doing per Scene resizing; <- not possible in Hybrid). So for resizing I would probably go for NNEDI3 as resizer and try whether it helps to so a stepped resizing.

Cu Selur