Tranferring files to new Imac

Welcome to the Apple Support Communities.

The best way is to create a Time Machine backup, then restore that backup following these steps: Setup Assistant and Migration Assistant - Apple Community.

For Time Machine, you need an external hard drive. Apple sells external hard drives, such as the LaCie Rugged USB-C + USB 3.0 Portable Hard Drive - Apple. Regardless of which drive you choose, it needs to be formatted. Follow these steps:

1. Go to Disk Utility (Finder > Go > Utilities)
2. In Disk Utility, select “View” > “Show All Devices”.
3. Select the top and non-indented drive in the external section of Disk Utility that matches the name of your external drive. 
4. Click Erase
5. Name: any name you want
6. Format: Use Mac OS Extended (Journaled) if you are using macOS Catalina or earlier, or APFS if you are using macOS Big Sur.
7. Scheme: GUID Partition Map
8. Click Erase

Finally, setup Time Machine: Back up your Mac with Time Machine - Apple Support.

Cheers,

Jack

Very simple, please follow the steps in Setup Assistant and Migration Assistant. If your old Mac does not have a Time Machine backup then please create one. You can use the same EHD for backing up the new computer. I'd suggest getting a OWC Mercury Elite Pro for backup and if necessary another for additional external storage. These EHDs are what most experienced users on these forums use due to their high reliability, great price and the vendor only sells products designed for Macs.

If you use the TM process it will install everything. You may want to diagnose the issue on old Mac first if at all possible