This games reviewer on Twitter suggests late submissions are still being taken, perhaps someone can confirm? (perhaps only if itch.io can hold up!):
https://twitter.com/DominicTarason/status/1501000030374842369
Viewing post in Bundle for Ukraine - call for submissions
Just to let you know please give me a heads up, I would totally give a pile of my games for free or cheap cost etc. for a fundraiser that's a good cause! I never knew itch or people did this, if there is anything to donate I would, but this round I paid the $10 for the bundle to do my part to help out the cause, I don't have a huge library of games but the next disaster in the world to come along I likely can gift away 10 ish for their cause.