I ran terraria 1.3.5.1 on gentoo linux with Radeon HD 6450. It ran slowly.
I didn't know HD6450 was not good enough for Terraria.

What is the minimum recommended GPU requirement for Terraria?

From the recommended specs: Video Card: 256mb Video Memory, capable of Shader Model 2.0+

Terraria doesn't depend on your GPU at all beyond that, so if the game doesn't run well you likely have another issue.

You could try:
- updating FNA https://forums.terraria.org/index.php?threads/massive-performance-improvement-mac-and-linux.78176/
- playing through Wine to check if there's any difference.

After updating FNA, there is some performance improvement. But, I still can't play terraria smoothly on high settings.

I could not execute terraria through wine due to the following error.

> env WINEPREFIX=/mnt/data/Games/gog.com/Terraria-wine wine 'C:/GOG Games/Terraria/Terraria.exe'
0009:fixme:ntdll:NtQuerySystemInformation info_class SYSTEM_PERFORMANCE_INFORMATION
0009:fixme:d3d9:D3DPERF_SetOptions (0x2) : stub
* Assertion: should not be reached at /vagrant/mono/mono/mini/mini-codegen.c:1453


abnormal program termination
0009:fixme:msvcrt:__clean_type_info_names_internal (0x3843980) stub
0009:fixme:msvcrt:__clean_type_info_names_internal (0x3597028) stub
0009:fixme:msvcrt:__clean_type_info_names_internal (0x2f99264) stub
0009:err:mscoree:expect_no_runtimes Process exited with a Mono runtime loaded.

Why aren't you just running the native Linux version?