What exactly should happen during flowering stage?

to mee it looks like you are in week 4 or 5 from flowering, but im not an expert. https://www.royalqueenseeds.com/blog-the-flowering-stage-of-cannabis-week-by-week-n611 the added pictures helped me alot in the beginning. after you went trough this material I would read up about trichomes. which will prepaire you for your next step.

Mandal Seeds have a fantastic "grow guides" section on their website, you will find lots and lots of great information. Often when flowering, some plants will start then seem to stop for a while before then exploding away to finish, it all has to do with hormones. Other plants just grow steadily and others grow in "spurts", as in stop/start.

Looking over your diary, it seems your plant was a bit delayed entering flower than you'd expect but it's progressing. The first few weeks of flower is all stretching and creating new budsites, usually in the 4th-6th weeks of flower is when the bulking really kicks in. Of course it's all strain dependant too, some are faster and some are slower. I wouldn't give up on it yet, those flowers will start fattening up soon.

Its looking good to me. Flowers will start to grow and then bulk up over time. Normally the stretch is happening in the first few weeks of flower. then they fill out and the end is bulking up. Good Luck!

Check out, Homegrown TV on YouTube, he has loads of videos seed to harvest.