According to the data lists of each keyboard (version D0 for MODX's latest firmware and version A0 for MODX+ release firmware - of which there is currently no update) both keyboards have the same Performance. Both have 2227 Performances (which is suspiciously close to this "227" number you've written) and the last page of Performances - where I would suspect differences - are identical.

No new Performances. I don't know what manuals you were referencing.

Here's what I referenced:
MODX: https://usa.yamaha.com/files/download/other_assets/2/1192592/modx_en_dl_d0.pdf
MODX+: https://usa.yamaha.com/files/download/other_assets/5/1583935/modx_plus_en_dl_a0.pdf

These links, like all, are temporary until Yamaha changes them - but good as of today.

What you did gain is polyphony on FM-X (now 128 where previous FM-X polyphony on MODX was 64) to match Montage's and waveform memory (1.75GB to match Montage's sample memory), and a new rubberized modwheel also the same as Montage's.

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not spam

I know from the manual and some Youtubers that there are 227 new preset Performances.

Post links to your sources for that info.

Just because it is on the internet doesn't mean it is true. This video is someone from Yamaha demoing MODX+ and it says there are new sounds.
https://www.youtube.com/watch?v=qHz7K3sWFqo

You can tell from the perf name displayed that all the sounds being demoed are on the Modx and listed in the Modx Data List doc.

Is there a way to quickly find the new ones in the menu?

Try a category search using the 'Preset' bank and page to the very last page.

On the Modx the last five performances listed are:

1. Drone Generator - (perf no. 2227)
2. Init Normal (AWM2)
3. Init Normal (FM-X)
4. Init Drum
5. Multi/GM

The latest data list doc for Modx has the last perfs listed as numbers 2196 - 2227 (Drone Generator) and they all have '*1' referencing this note at the top of the performance list
MODX Data List 2

*1 The new Performances added by firmware version 2.50 update

Is there a complete list of the new Performances?

I am not aware of any new performance presets.

As seen above a footnote was added to the doc to indicate the new performances added in the 2.50 update. Yamaha may not ALWAYS do that and it isn't guaranteed the any added new perfs would begin with perf no. 2228, 2229, etc.

Thanks, guys. I just realized that the new 227 presets were also available in MODX, since OS 2.51

MODX v2.5 added 32 new Performance presets. As I mentioned before, I think this "227" stuff is coming from the total number of Performances (2227).