James,
When I'm editing a larger project I prepare it in sections, each one a separate project. I then use "import" (as in the link above) to assemble them one at a time. This allows me to work with smaller units and troubleshoot them individually. As tomasc noted, I then save the ever-growing master project under an umbrella name.
Main thing to note is that the new project will be inserted on the timeline wherever your timeline slider happens to be positioned, so be sure you've thought that out first.
Regards,
Dan
Power Director 21-Ultimate
v 21.0.3111.0
XPS-8940, Win-10 64-bit,
Intel Core i9-10900 processor
(10 core, 20M Cache),
32GB DDR4 RAM, 2TB M.2 PCIe NVME SSD, 2TB 7200 RPM SATA HDD,
NVIDIA GeForce RTX 2060 SUPER 8GB GDDR6