You aren't missing out on gameplay! The Compatibility version receives the same content updates as the standard version and supports multiplayer with standard-version players.
Your PC has limited RAM (4GB or less) or an older integrated graphics card that struggles with new rendering updates. Stardew Valley Compatibility Version Download
Right-click the game and select > Configure . You aren't missing out on gameplay
is a vital "legacy" branch. This version uses the older 32-bit XNA framework instead of the 64-bit MonoGame framework introduced in the 1.5.5 technical update. Why Use the Compatibility Version? Stardew Valley Compatibility Version Download
When downloading mods from Nexus Mods, do not blindly click the "Main File" download button. Navigate to the tab of the mod page. Scroll down to the Old Files or Archived Files section.