I believe it was this forum where once read "oncidiums are ugly blooming machines".
If it makes you feel better, here's a recent pic of my ratty Onc. Twinkle Pink Profusion, purchased with much better looking leaves and one spike in Aug. 2020. It looks like hell, but gained six new spikes.
How cold is that windowsill? Could it be cold damage?
Look it up on bluenanta.com. Find the ancestors. Look them up on orchidspecies.com and look at their temperature preferences. It might be a combination of low humidity and temperature.
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