If bonding 2 different connection types, does it add the bandwidth or is it limited by the slowest?

Just a theoretical question for my own knowledge. Let’s say you have 2 WAN connections, the primary is 25/10 DSL and the secondary is 5G which on average gives 100/60.

If I bond those 2 together, I know there’s overhead and other losses but just for illustration purposes, is it supposed to give 125/70 as in adding them up, or is it impacted by the slowest connection at all, as in I’d get 50/20?

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