I don’t know if the needed contents of .htaccess file can vary per hosting server (e.g. if Apache is configured differently, or different Apache versions), but looking at project files from one UE4 project that did use .htaccess with Apache, it seems to have the following in it:
AddType application/x-javascript .jsgz
AddType application/octet-stream .datagz
AddType application/wasm .wasm
AddType application/wasm .wasmgz
RewriteEngine on
# If client accepts compressed files
RewriteCond %{HTTP:Accept-Encoding} gzip
# and if compressed file exists
RewriteCond %{REQUEST_FILENAME}gz -f
# send .extgz instead of .ext
RewriteRule ^(.+)\.(mem|js|data|symbols|wasm)$ $1.$2gz
AddEncoding gzip .jsgz
AddEncoding gzip .datagz
AddEncoding gzip .memgz
AddEncoding gzip .symbolsgz
AddEncoding gzip .wasmgz
Though I have not tested or deployed this project in practice to verify it first hand.