To me it sounds like your battery has failed. This happens occasionally as with every batch there are at least a couple bad ones. I've replaced quite a few batteries and have had the same problem where they're fine at first but begin to fail within weeks or months. I suggest you request a warranty replacement through iFixit. It won't hurt and it's really the only way to narrow down the issue (assuming you've already discarded your old one). It's likely a coincidence that it began having issues after Ventura. Best of luck!