Hi Max,
We checked the log and found out that the mod security in your server blocks this function:
[Wed Feb 16 10:00:15.525787 2022] [:error] [pid 25113:tid 140421296531200] [client 193.32.85.252:45772] [client 193.32.85.252] ModSecurity: [file "/etc/httpd/conf/modsecurity.d/rules/tortix/modsec/50_plesk_basic_asl_rules.conf"] [line "250"] [id "33340147"] [rev "134"] [msg "Protected by Atomicorp.com Basic Non-Realtime WAF Rules: Potential Cross Site Scripting Attack"] [data "<script"] [severity "CRITICAL"] Access denied with code 403 (phase 2). Pattern match "(?:<
?script|(?:<|< ?/)(?:(?:java|vb)script|about|applet|activex|chrome)|< ?/?i?frame|\\\\%env)" at ARGS:data[other_code_share]. [hostname "rivoluzionecopernicanalazio.it"] [uri "/administrator/index.php"] [unique_id "Ygy9H8@iQkEnGwQNZtJ6cwAAAMc"], referer: https://rivoluzionecopernicanalazio.it/administrator/index.php?option=com_templates&view=style&layout=edit&id=9
Could you temporarily disable this mod in your server side or contact your hosting provider for help to add exception for template?