You can follow the guide here and in section "Step 2. Modify your Confluence server.xml file", add TLSv1.3 to the sslProtocols and sslEnabledProtocols attributes.
While the above-mentioned guide will enable direct SSL configuration in Confluence, best practice is to use a reverse proxy (such as Nginx or Apache) and do the SSL configuration in the proxy server, rather than in Confluence directly.
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