I don't exactly know why but over the past few days I've gone from about 30-50 spam emails a day to, just now, 250! But, thanks to SpamSieve, I don't have to mess with them, other than to quickly scan the list and delete them immediately. And I only scan the list to make sure nothing was mis-marked. And it hasn't been. You can check it out at: https://c-command.com/spamsieve/.
There's a free download and trial and given the amount of time and hassle it has provided me over many years, well worth the price. Plus, if you use IMAP and your iPhone or iPad to access and deal with emails, it cuts down on those that end up on either device. That is because the marked spam is shifted to a spam folder on your Mac, not retained in the IMAP accounts, so spam doesn't end up on your other devices. And I honestly don't recall any false positives, but SpamSieve tells me there have been 3 since May.