Hello.
I need to echo what the other poster has said. I replaced my exhaust manifold, cat, and both O2 sensors late in 2020 and after this I saw code 0420. I fixed this by checking the O2 sensor connectors (where I found that one had come loose) and then resetting the codes (detatching battery overnight should do it).
Since you're asking on a forum, and despite the fact that I'm not a mechanic, I'd advise that it's likely that the blinking CEL reflects irreversible damage being done to your engine. I've seen it in other vehicles when the oil level gets low enough that the engine can no longer reliably lubricate the moving parts to the proper degree. Maybe another issue is causing it, but I think anyone here with a basic knowledge of cars will advise that driving and not having a mechanic take a look is going to cause further long-term damage.
Best of luck.