diretonic
This is a very important point for people starting out on their journey like @Sophia & @WieWaldi. It's daunting when you hear a great player improvise. I remember when I was younger (many many decades ago) hearing people playing blues and boogie and thinking how on earth are they doing that without any sheet music.
The reality is that most improvisations aren't that original. I've mentioned this quote before over on PW. I heard Dave Brubeck interviewed in a documentary, probably back in the 1990s. He was asked how he continued to come up with improvisations after all this time (or something akin to that). His reply was a reality check for me. He said "How much is improvised when you've played the chord sequence a thousand times". I can't remember whether he was talking specifically about blues in the interview. But the same applies, even to advanced Jazz pianists.
It's similar to reading music. The first time you sight read a piece, depending on it's difficulty you may struggle badly, but as time goes by you get more and more fluent, and eventually you'll play the piece well, and in some cases memorise it. Improvisation is similar, the more vocabulary (blues scale, modes, chord tones, tritone subs etc etc) you add to your arsenal the more original your improvisation will sound. In other words both are muscle memory to a degree.
So once you know the 12 bar form, and can string a few licks and riffs together you will start to sound like you are improvising. And with a lot of practise you will eventually start to find original licks and phrases of your own. Well you'll think they are your own, but the reality is that someone somewhere has already done them!
My version of Beale Street sounds like there is some improvisation in it. In reality in the solos it's probably 95%+ stuff I've played before. It would have been 99%, but I don't improvise blues in Bb very often, so there may have been some spontaneity there.
End of ramble!