I used to be very good (not blowing my own trumpet here, oi oi), but I feel I missed an opportunity by not joining a club. Likes @japes says, going out with stronger folk is the best improver. They’ll hit the climbs harder and quicker and you’ll surprise yourself when you keep pace with them. It hurts, but you’ll do it. Then you’ll do it the following weeks and it’ll be easier. Then you’ll meet more like minded people who aren’t weridos off the internet.
If you have the motivation to sit on a turbo for and hour every other day, that’s cool and turbo helps, but you’ll never replicate the outside roads with Zwift or whatever.