This exists, kind of

There’s bonded connections in several senses

Bonded ports but this doesn’t increase throughput in the way you’re thinking. eg if I bond 2 1 gigabit Ethernet ports I can’t connect at 2 gigabits, I can connect 2 users at up to one gigabit each (or several users totaling 2 gigabits but no 1 user at more than 1 gigabit)

bonding routers can take two internet connections and combine them, which is closer to what you are probably imagining. They combine throughput, eg a 100mbit connection and a 100mbit connection become a 200mbit connection although realistically it’s not that perfect and you have to get the right services for it, not just any connection will work, it’s a rabbit hole and generally much slower and worse latency than if you just got a traditional connection. Think people using starlink and 5g internet in rural settings

There’s also something called speedify, which is software that claims to do the above in software alone, bonds two connections to combine throughput. Never tried it, reviews are mixed. Some say it works, some say it’s spotty, some say you only get the speed of the one connection, etc.