With pg16 the \bind command was added to psql

\bind [ parameter ] ...
Sets query parameters for the next query execution, with the specified parameters passed for any parameter placeholders ($1 etc.).

Example:

INSERT INTO tbl1 VALUES ($1, $2) \bind 'first value' 'second value' \g
This also works for query-execution commands besides \g, such as \gx and \gset.

This command causes the extended query protocol (see Section 55.1.2) to be used, unlike normal psql operation, which uses the simple query protocol. So this command can be useful to test the extended query protocol from psql. (The extended query protocol is used even if the query has no parameters and this command specifies zero parameters.) This command affects only the next query executed; all subsequent queries will use the simple query protocol by default.

This is extremely helpful when debugging sql that you've copy pasted from a project or app.