I think nowadays some people (specially US players) are actually quite serious when it comes to play money at stars. I don't think it's good way to learn poker tho, because money is only way to measure whether your actually winning or loosing.
I actually think someone who is just starting out should invest around same amount which they willing to use for 1 saturday night out (approx. 20€ - 300€ for most people). You should try different games and try to found if there's game you want to seriously commit to be good at. Idea is to invest amount enough to be serious about winning or loosing, but not so much that it will pull you back financially. I think after that if you working on regular job, you should start to make monthly deposits with fixed amount €/month and try to turn that on profits.
If you actually serious about winning you might consider to hire a coach or join for staking stable for some time. After you start winning you should build your bankroll by playing game which you plan to play as your main game.... If you operating with low bank (less than 5k€) you will benefit a lot from taking advantage of all promotions where pokersites basically give away free money... For example partypoker use to have this promotion where they basically give you free tournament ticket between 1 - 215$ every day (if remember correct). So you want to keep your eyes open for those. Lot of promotions are as well non poker related, but easy way to build bank. You can find sportsbetting bonuses, freebets which are fairly easy to rollover with very low risk involved if you use matched betting / arbitrage betting approach where you basically cover all possible outcomes of the bet by betting on several bookies.
I would personally recommend anyone who is beginner to start in some form of tournaments... I've seen lot of people starting out during last 1 - 2 years and made lot of success in short time focusing in this formats. Whether it's MTT, SNG or Spin & go it's very likely that these formats will remain softest games and relatively soft to beat in future as well, while cash games start to be tougher and tougher to beat because of the continually rising high rake and fairly knowledgeable playerpool.
What will most effect whether you win money or not is 1) games you will play 2) how you execute the process. To learn and win poker you need to be actually spending lot of time to PLAY poker, while in the beginning you might want to have 80% study / 20% play rate, it should turn around to 80% play / 20% study when you improve a bit. If you are crushing like 10bb/100 at any level you should really not spend that much time for studying anymore until your winrate starts to decrease or you move up for higher level.
Studying is good when it's practical. When you study you want to do it effectively, don't waste too much times on things that will not have so much effect for your winrate / ROI. If you spend too much time in things which don't really matter or play format which is basically a rake trap for beginners you can just forget moving up in stakes. Playing some of the games such as NL2 zoom or working balanced river c/r range with GTO solver while playing these games are good examples for this. If you are paying more rake than your winning from the games, getting close to 0% rakeback --> you're probably playing the wrong game no matter how good you are.
If you working on a leak that by plugging will not make big difference --> There's probably bigger leak exist which should be your main attention. Biggest leaks are often small ones which will come up frequently. Always keep 1 - 3 main points for studying... Example could be "check/raising flops". Let's say you study and notice that you should be c/r more. You might write yourself note which could be simple note such as -> "c/r more" or more complicated --> "c/r more BDFDs, gutshots on dry boards when face cbet against LP raiser on the BB". When you learn new things, keep note of them and practice bit by bit it comes automatic and you can move to next key point in your game.
Good luck.