""who uses as a local email client in 2023. Doesn't everybody use webmail these days?"
Well to be honest, yes, most of us do,"
What parallel universe do you live in? I know very, very few people that use webmail as their primary access to mail. Everyone at work uses Outlook and those at home not on PCs use Mac Mail.
I've got several email accounts and whilst I have set up Edge and Chrome profiles for each account, I still use Thunderbird for my personal email accounts and Outlook for my work ones. I even use Windows Mail for my burner email accounts.
Gmail is okay for reading and writing the odd email but it's totally pants at mailbox management. Heck, you can't even sort by subject or sender email address and deleting multiple emails at once is immensely tedious compared to a real email application.