Apple has released iOS 13.2.3 and iPadOS 13.2.3. Go to Settings > General > Software Update on your iPhone and/or iPad to install them.
According to Apple’s release notes, the updates:
° Fix an issue where system search and search within Mail, Files, and Notes might not work;
° Address an issue where photos, links, and other attachments might not display in the Messages details view;
° Fix an issue that could prevent apps from downloading content in the background
Resolves issues that may prevent Mail from fetching new messages, and fail to include and quote original message content in Exchange accounts.