My solution for climbing hills is to downshift early into lower gears and to pedal slowly. This gets me to the top slowly but without having to stop and recover or walk the bike up the hill. Usually I have to fight the instinct to pedal fast in lower gears. The way I do that is to watch my speedometer.

For example, there's a steep hill around here I often have to climb. I know from experience that I can make it all the way to the top without stopping if I climb it at around 3.5 mph. I'll be breathing deeply but not gasping. Instinct always tells me to try to take the hill at 7-8 mph, but if I do that, I'll blow up before I finish the climb and have to stop & recover. It's a real mental struggle to downshift and slow down. Watching my speedometer helps me pace the climb correctly.

My son used to use a heart rate monitor to pace himself when he was learning to climb steep hills. He paced himself so he was climbing at 70% of his max heart rate, no more than that. You have to have some way to pace yourself correctly when climbing hills. It can be a heart rate monitor, or a speedometer plus experience with that particular hill, or just climbing at speeds that don't exceed your ability to pump oxygenated blood to the leg muscles.

The only real problem with taking hills that slow is that you start wobbling below about 4 mph. I've found that the wobbling at slow speeds gets somewhat better with practice.

You should be able to ride up any hill you can walk up. You may have to ride at walking speed, though, and it's sometimes a challenge to maintain your balance.