Step-by-step?: How to migrate parts of the Home folder to another PC?

Question

I'm requesting step-by-step help, as I'm an Ubuntu user, not a computer systems/software person. I can follow explicit detailed instructions for Terminal commands. (For example, I do not know how to move between different directories in Terminal.)

I have searched and have not found explicit step-by-step instructions for a proper way to move over contents of the Home folder in an old PC (running LUbuntu 18.04.5 LTS) to the Home folder of a new PC (running Ubuntu 20.04.2 LTS).

During my (unguided) attempts at the moving-over process so far, I have deleted and tried to replace most of the contents of the new Home folder. So I think that the new Home folder is messed up by now.

I want to move across:

• my data files (music, photos, documents, videos, desktop, downloads, etc.)
• all personal content, settings, etc. from my old programs, including from Firefox (bookmarks, history, extensions, open sessions, etc.), from Thunderbird (accounts, local folders, etc.), from Zoom, and other programs that I will try to use again in future.

Immediately after I installed Ubuntu 20.04.2 LTS from a disc to a new PC, the OS seemed to behave well. (By the way, the internal HDD in the new PC has over 200 GB unused space.)

Next, I ran into trouble, trying to migrate over a copy of the files and folders from the Home folder in my old PC (which is running LUbuntu 18.04.5 LTS).

Here's what I did, and what went wrong.

FIRST I BACKED UP (MOST PARTS OF) MY OLD HOME FOLDER.

• I opened my old Home folder in a window of PCManFM 1.2.5 (the file manager).
• I selected 'Show Hidden Files'.
• I did Select All (items in the window), and then de-selected the large folders that contain videos (which I plan to migrate to the new PC later).
• In a second window of PCManFM 1.2.5, I created a new folder in an empty external HDD, then named it (not with name 'Home', and not with name Username), and then I opened the new folder.
• I dragged all the selected items from the first file manager window and dropped them into the second window.

I TRIED TWO WAYS OF MIGRATING OVER THE CONTENTS OF THE BACK-UP HOME FOLDER.

1. In File Manager in the new PC:

• I did 'Select All' in the back-up home folder in the external HDD.
• I dragged the selected contents, and dropped them into the Home folder in the OS in the new PC.
• When prompted, I opted to merge those new and old folders which had the same names.
• After that, I found I could open my browser or the Image Viewer program, but then the resulting window of that program would be empty and unresponsive, and in fact the new PC would be frozen. And I had to do a hard restart in order to repeat the attempt to run a program.

• After (1) above, I deleted everything in the Home folder in the new PC (except .local, .config, and .cache, which did not seem amenable to being deleted).
• Then, similar to what I had done in (1) above, I did 'Select All' in the back-up home folder in the external HDD. Then I dragged the selected contents, and dropped them into the Home folder in the OS in the new PC.
• When prompted, I opted to Skip All when asked about merging new and old folders having the same names.
• There were some other prompts. And similarly, I opted for Skip All.
• After that, my browser loaded and worked for a few minutes before freezing.
• After a hard restart, I opened Image Viewer, which froze.
• After another hard restart, I opened an image file in GIMP, which seemed to work with a few filter operations that I tried.

I'm wondering whether I should try deleting the Home folder in the new PC, and if successful drag the back-up folder from the external HDD into the same place. If so, should I rename that folder 'Home'?