My understanding (and also in the understanding of several well-known HR experts) of employee motivation is that is a vital thing, but there's a hidden part that is always worth starting with: minimizing instances of demotivation. It's like going down the mountain to ski, you first have to climb up the chairlift.
This is not a case study and certainly not a how-to manual. It is simply a series of disparate principles and theses that I adhere to in team management.
What can demotivate team members?
When working conditions (e.g., an 8-hour workday) only apply to part of the team members.

Lack of feedback from the lead.

Comparison with other employees

Intolerance for mistakes. Also constant reminder of them.

Lack of confidence in new or important projects. (By the way, inability to delegate also demotivates).

A poorly functioning system of appeals and decision making. Why did the product marketer develop the concepts of improvements at all, if he is waiting for an uproar for 2 months, why should he get so much involved in the project, if his lead is not involved at all?

Micromanagement. It's a tricky story, especially for young employees or teams. I prefer "let's meet after the first iteration of the project and share our findings tomorrow at 2 p.m." to the constant "what's up, how's the task?" in person.
Principles I use to increase motivation in my team:
Regular rallies to synchronize tasks. Because of frequent collaboration with development and design, the most effective marketing team flow is by sprints. Frequent but brief reporting and synchronization allow the team to keep its focus on the highest priority tasks.

Retrospective. In my opinion, generally the most important part of communication between team members and the lead. In turn, each employee only shares the emotional aspects of completing certain tasks, answering questions: what tasks were easy, what would you like to repeat, and what, on the contrary, you did not want to do, the answers are analyzed and the most elegant and environmentally friendly solution is offered.
For example, one of the team members was dragging on and on about a promo concept for one of the projects (he didn't feel inspired, and couldn't think of any creative way), we analyzed his feelings in retrospect, and it turned out that the most demotivating thing in this task was waiting for an uproar from the team leader, which included endless corrections and making comments on questions that we had not noticed before. As a result, we added a small regulation on the number of edits and deadline for uproots to the concept docs.

One-to-one meeting. Regular face-to-face meetings with an employee give the subordinate the understanding that he has a time and a place where he can give feedback on his tasks, the company, etc., as well as get feedback on the work from the manager, update goals and objectives and identify points of growth.