My husband wanted me to post this. I have no idea how to help with this, so any questions, keep in mind I do NOT know any fixes. He does, but he barely plays the game. . He spent a few hours until he read NKSHV's post, and he was so appreciative he posted the following:
I posted this question on the terraria steam community forums but got no answer: How can you launch the 64 bit version of Tmod loader? Before the final update, you simply replaced the vanilla terraria files with the 64 bit tmod loader ones but as we all know, this is not possible anymore. So...
forums.terraria.org
Thank you NKSHV from post #694 on Wednesday at 10:50 AM (This just expands his or her post... don't know you but I think you gave the best answer)
The installation is in fact even easier - just unpack tmodloader 64 to any empty folder, move to that folder:
content folder from steam tmodloader
and than content folder from steam terraria without replacing and that is it.
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* Tested on 5/25/2020 and might break if there are any updates (worked as of 5/25/20)
* Install tModLoader from Steam if you haven't already for step 3
* Get a copy of Terraria before it was upgraded so you can copy the content directory on step 4 (I didn't take the time to upgrade it to version 1.4 to see if it breaks but the earlier version works fine / someone else can test if they've already upgraded to 1.4 to see if it works with no issues) *As long as it's LEGAL*
1) Create a new Terraria directory (example C:\Games\Terraria)
2) Extract Archive-e298.zip (That's your 64bit branch of TModLoader that's at the beginning of the thread)
3) Copy the tModLoader Content directory in your tModLoader folder (something like C:\[YOUR_STEAM_DIRECTORY]\steamapps\common\tModLoader which you can get from tModLoader Properties -> Local Files -> Browse Local Files...) / File named tModLoaderContent.zip
4) Extract TerrariaContent.zip which is my wife's Terraria Content directory that she didn't update to 1.4)
5) Launch Terraria.exe from the new Terraria directory (example C:\Games\Terraria)
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Bonus (how to create a Desktop Shortcut or Start Menu icon... lots of ways to do this so I'll give a working example):
Find the Terraria.exe file in your Terraria directory like C:\Games\Terraria\Terraria.exe and right click then Send to Desktop (this creates your desktop shortcut)
Go to your Desktop and locate that Shortcut then right click to rename it to Terraria if you want (this gets rid of extra wording on the shortcut but isn't required)
Use that icon to launch Terraria
* You can also right click on that desktop shortcut icon and select Pin to Start then delete the desktop shortcut icon if you prefer to launch it from your Windows 10 Start Menu (not necessary but cleaner in my opinion)