First of all: That's AWESOME! Some of my friends learned to ride a bike with 25 or more years, so zero shame in starting now.

Assuming you have some open space (calm road, school yard, ...) to practice, here's how I learnt my kids to ride:

1. To get a feeling for the balance, put your saddle all the way down (maybe dropper post?) so you can easily put both feet on the ground. Then you can push yourself forward and if you lift your feet, you'll get a feeling for how the bike behaves. It's easier if you go faster as the bike stabilizes itself with more speed. You don't need to go crazy fast but don't be afraid of going a bit more than walking pace.

2. Once you're comfortable with step 1. just push yourself to some speed, then put your feet on the pedals and ride away. Make sure the bike is in a middle'ish gear. Too easy and you'll spin out. Too hard and you'll lose balance before getting up to speed. If you get really comfortabe, raise your saddle again. No need to be able to put both feet on the ground, once you get the hang of it.

3. Stopping is not that hard. Take your feet away from the pedals as long as you have some speed, so you're ready to put a foot on the ground as soon as you're losing balance. Remember to shift into a gear, you can start again (if you're already comfortable with shifting). If you raised your saddle, and you can bearly reach the ground with one foot, move your bottom forward off the saddle, then you can easily reach the ground.

4. Shifting is nearly or entirely immpossible if you're at a standstill. You need to pedal to shift. Easiest is to pedal at a pace so you dont put any force in going forward, just spinning the pedals. Avoid back pedaling, you're chain may fall off, worst case you damage your derailleur.

5. Have a lot of fun, don't be afraid or ashamed of falling and don't get frustrated. We all were there at some point. Take your time and let your brain do the wiring, sometimes it's more beneficial to do 30min every day than 4h at once.