Haven't seen this widely reported or spotted a thread here yet:
I'm told this is to do with two factor authentication. There were certain PS1/PSP games which would only play on Vita through PS3 transfer, I'm not aware that PC allows you to download these games and transfer them onto your Vita therefore there's no legitimate* way to get these games onto your Vita any more. Stuff like Burnout Legends, Metal Gear Solid & Silent Hill (all NA) are among the games that required PS3 transfer.
Another case where Sony have retroactively done something without announcing it ahead of time, I would've moved a couple more games
Important notice
Find out which features are no longer available on your PlayStation console.
www.playstation.com
From May 11th, 2022 content cannot be transferred from PS3 consoles to PS Vita systems. Content can still be downloaded directly to PS3 consoles or PS Vita systems or it can be transferred using a PC.
Existing PlayStation Plus subscriptions will not be affected by these changes. You can access and download all of your existing PlayStation Plus content. Additionally, you will still be able to access your already purchased content from your respective devices.
I'm told this is to do with two factor authentication. There were certain PS1/PSP games which would only play on Vita through PS3 transfer, I'm not aware that PC allows you to download these games and transfer them onto your Vita therefore there's no legitimate* way to get these games onto your Vita any more. Stuff like Burnout Legends, Metal Gear Solid & Silent Hill (all NA) are among the games that required PS3 transfer.
Another case where Sony have retroactively done something without announcing it ahead of time, I would've moved a couple more games