If it’s a path problem (no details to say), I suspect GUI bug is fixed in next Stable,
because it seems already fixed in 2.2.1.0_beta_2026-03-05 which is a candidate.
You then tell Duplicati where your rclone is. For example, on this PC mine is here:
I doubt that the Duplicati team will ever try to track all the changes rclone does.
Configuration by rclone config or a GUI you find can be used to config remotes.
Once you have set up an rclone remote, just tell Duplicati the name you picked.
Keep in mind that rclone remotes are per user, so switching can cause problem.
Even rclone has long had trouble coming up with GUI, but I see a new one out.
Please note that rclone is not backup software. It doesn’t keep old file versions.
If virus or manual accident damages some files, going back may be impossible.
I assume your remote is not one Duplicati supports, thus forcing you into rclone.
If the Duplicati destination is directly supported, you should usually just use that.