MySQL: 1:n relationship with auto increasing PK - mysql

Question

I've two tables: users and files. A user can create files (1:n relationship).
When a user is deleted, all the user files refered to the user should be deleted, too. Deleting single files of a user should also be possible.
Try 1
CREATE TABLE `users` (
`user_id` INT NOT NULL AUTO_INCREMENT,
`name` VARCHAR(50) NOT NULL,
`password` VARCHAR(60) NOT NULL,
`salt` VARCHAR(33) NOT NULL,
`user_group_id` INT NOT NULL,
PRIMARY KEY (`user_id`),
CONSTRAINT `fk_u_user_group` FOREIGN KEY (`user_group_id`) REFERENCES `user_groups` (`user_group_id`) ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
CREATE TABLE `user_file` (
`user_id` INT NOT NULL,
`user_file_id` INT NOT NULL,
`name` VARCHAR(50) NOT NULL,
`content` JSON DEFAULT NULL,
PRIMARY KEY ( `user_id`, `user_file_id`),
CONSTRAINT `fk_uf_user_id` FOREIGN KEY (`user_id`) REFERENCES `users` (`user_id`) ON UPDATE CASCADE ON DELETE CASCADE
)ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
The table user_files contains files of all users so the primary key have to be a composition of user_id and user_file_id.
This solution works for me but there is one problem: The user_file_id is not increased automatically (because it's not the primary key). But I do not want to know the user_file_id when inserting new files to the table.
INSERT INTO user_files VALUES(1, ???, 'New file', default)
The default keyword instead of ??? is not working here.
Try 2
Another solution I though of would be to create a new table user_user_files that merges the tables users and user_files.
CREATE TABLE `user_file` (
`user_file_id` INT NOT NULL AUTO_INCREMENT,
`name` VARCHAR(50) NOT NULL,
`content` JSON DEFAULT NULL,
PRIMARY KEY (`user_file_id`),
)ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
CREATE TABLE `user_user_files`(
`user_id` INT NOT NULL,
`user_file_id` INT NOT NULL,
PRIMARY KEY(`user_id`, `user_file_id`),
CONSTRAINT `fk_uuf_user_id` FOREIGN KEY (`user_id`) REFERENCES `users` (`user_id`) ON UPDATE CASCADE ON DELETE CASCADE,
CONSTRAINT `fk_uuf_user_file_id` FOREIGN KEY (`user_file_id`) REFERENCES `user_files` (`user_file_id`) ON UPDATE CASCADE ON DELETE CASCADE
)ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
With that I could create a trigger when inserting a new row into user_files and that trigger would add a new row to user_user_files.
DELIMITER $$
CREATE TRIGGER after_user_insert
AFTER INSERT
ON user_files FOR EACH ROW
BEGIN
INSERT INTO `user_user_files` VALUES(NEW.user_file_id,default, default);
END$$
DELIMITER ;
But is this possible when I want the following behavior?
Delete all user files when the user is deleted
Option to delete single user files from a user
Summary
So with try 1 there is the problem that the primary key is not increased automatically.
With try 2 I do not know if my desired behavior works with deleting / adding rows.