@scottyboyyy tip: don't worry, be happy. Live below your means. Jump into the next thing as you're confident you're ready.
There's a lot of change that happens between leaving high school and starting actual careers. I went through college, met a girl, and had to move several hours away to take my big-boy job. Then engagement ring and wedding shortly after her college graduation. Cash in the bank is great for all this. Anything invested can lose value, so only be investing money you KNOW you will not be using before you're 30.
Credit cards: they are bill driven. if you get a credit card, the best strategy is to pay the bill once a month, in time, in full. The danger with credit cards is they want to suck you into using the card to buy for more than you can really afford, and you end up in a bind with high interest debt.
Credit cards are good for building a credit history...and you have a little bit more control in case of dispute. But a debit card operates mechanically the same with purchases -- it's just the money comes directly out of your bank account instead of getting billed for the total of credit card charges once a month.
Look into HYSA -- High Yield Savings Accounts. I use Discover Bank for a 4.35% savings account, plus CDs.
So, 20YO, what about you? Are you living at home with the parents? Completely separated from parents and funding your own life? College? Trade School? Working / starting a career?