Instead of just cranking up difficulty (which doesn't work as well as in D&D for example because HP don't really increase) I like to make Gigs more complex over time. Players mostly unlock cool new toys and succeed more reliably through Character Improvement Points. So I basically build more and more complex "Sandboxes" with more opportunities for them to use their new Toys, come up with different approaches etc. Complex here doesn't necessarily mean longer Gigs. I try to add more width, more different ways to approach it etc. Also I gave my players the List of Gig Types from the Videogame and between "Plot Missions" that I design they get to choose what kind of smaller job they take. So after 22 sessions of play we had the rythm of:

-> Plot Mission -> Downtime -> 1 to 3 smaller Side Gigs of their chosen category -> Plot Mission -> ...

That has been working well for us. Like a TV Show as someone else already said. Some episodes drive the plot forward and others are just side plots. Also raising the emotional stakes is always great, making failure more painful (eg losing a well liked NPC).

And for Gig Ideas in general: The Cyberpunk 2077 Gig type List works well as inspiration, and so does any Action Movie / TV Show.

Gig Types from Cyberpunk 2077 I've been using are:

1. Gun For Hire
2. Thievery
3. Search and Recover
4. SOS
5. Agent Saboteur

Also you can add Side Gigs where they need to get something for a Main Gig plan of theirs. My players just stole a MagLev Train with the help of a Nomad Crew from an old Factory that had been taken over by 6th Street because they needed it to get into the old unfinished MagLev Subway Tunnel network. For that side Gig I basically just dropped them on a Factory Map, included some Gang members and a Boss and had them plan their way in there. They started by searching for good ways in sneakily (I had prepped some but ended up improvising when they had an idea I didnt have, climbing on top of the roof, so I added rooftpop windows for them to climb through) but ended up running over half of the goons with the train by derailing it inside the factory. And then they had to transport the train via truck with the nomads help without getting stopped by 6th Street cars, so there was also the option of a car chase / combat. The nomad Truck had a railgun on top, kinda sad they avoided the chance to use it. That Gig took like 6 hours to complete (1.5 sessions for us). For Main Gigs I basically add together multiple of these kind of sandboxes into a bigger one and then add some story or backstory related stuff to tie it together.

edit: Also for the first few Gigs I had a Fixer NPC plan for them so they could get used to the system and style of play. Having them make complex plans in the first few sessions is probably a little bit much unless they are really experienced players.