As of 2021, R* have added server-side checks for anyone earning more than you legitmately can, which is especially devastating for new accounts, which seem to get quite low tolerances. So, you're gonna have to try to be semi-legit, not greedy, and not over-doing it.
You can use Stand's "Gift Spawned Vehicle" feature on yourself to get some nice vehicular assets, following our guide here. However, if you decide to go selling your garage's new fillings, keep within the safe limits:
Not more than 2 sales per 2 real-world hours.
Not more than 7 sales per 30 real-world hours.
Cayo Perico Heist
Getting this heist set up is quite easy thanks to our "Quick Progress" options, and completing the heist itself will also be quite easy with the movement options or just good ol' teleporting.
Note that R* has implemented a limit that prevents you from earning more than $2.550.000 per run or more than $4.100.000 per hour from this heist.
If you're gonna use this as a means to mod money, please don't do it more than once per real-world day and/or keep the time from when you paid for the heist to when you finished the finale within reasonable limits.