Version 2026.56.6.11336.1236969, playing on PC (Windows client)
During a Brawl game, while we both have creatures, I held Restoration Magic in my hand with enough untapped lands to pay any of its costs. I let my opponent attack me, then choose my blockers. Then, I get the priority, can use an ability of an artifact I control, but cannot cast Restoration Magic at all. I drag it from my hand, but nothing happens.
My opponent had no specific permanent forbidding me from casting anything, nor had played any spell forbidding it (and me neither).
I just could not play that spell at all, but should have been able to.