I don’t know why Thunderbird can’t get a reliable, functional search ability. It’s such garbage. I constantly have to delete my entire search index and start from scratch, it is immensely frustrating.
The problems connecting to gmail are also so frustrating. Yes, they are Google’s fault but if you make an e-mail client you maybe need to add a workaround for the world’s most popular e-mail provider. It’s totally fixable because you can apply those fixes manually.