Max used 33 back in his karting days, I think. Generally the drivers have used numbers that they had back in the day at the start of their careers, unless an existing F1 already had that number by the time they arrived in F1.
Every team has a free number for FP1 outings. 38 was designated to STR. Any driver in that car during an FP1 session would have used that number.
The drivers choose the numbers though, not the teams, so no lol. Isn't Gasly 10? Seb is 5, although he only spent 1 year in RB after becoming "5" and he used the number 1 as reigning champion