Much more info here: https://denofthieves.nl/sir-you-are-being-hunted-patch-1-5-and-reinvented-edition
Condensed notes from Steam:
Key Features of 1.5
Multiplayer functionality restored and Official Multiplayer servers back online.
Mac 64-bit support. This should give a significant speedup on Apple machines with an M1 chip.
Islands generate much faster due to engine upgrade.
Many legacy bugs fixed and graphical upgrades including modern water shader.
The Full Details
Windows: Upgraded Engine to Unity 2018.3.2f1 (was Unity 4.6.1f1).
Mac: Upgraded Engine to Unity 2021.1.18f1 (was Unity 4.6.1f1).
Linux: Upgraded Engine to Unity 2021.1.18f1 (was Unity 4.6.1f1).
The Mac version of "Sir, You're Being Hunted" now has native 64-bit support for both Intel and Apple Silicon platforms. This should give a significant speedup on Apple machines with an M1 chip.
Terrains are now rendered using the new Terrain System. As a result, distant terrain should now look nicer.
Rendering has been changed so that the game now renders in the native sRGB color space. Contrast has been slightly increased as a result.
New graphics options have been added: an "Ultra" preset, MSAA Anti-Aliasing, an all-new "Ultra" setting for Water Effects and a toggle that enables SM 4.0 High-Quality Transparency have been added.
All Textures have been reimported at their maximum resolution. This results in a slight increase in texture resolution, notably on many buildings (churches and houses) in the game world.
The in-game HUD has been reworked to scale better on widescreen monitors (4:3, 16:9, 21:9 and tripple-wide 16:9 setups are supported). Texture resolution on UI elements has been increased and certain elements have been reworked.
The FPS cap has changed: when enabled, it will now lock to 120 fps by default (was 70). You can override this behaviour by launching the game with "fpslimit x" as a launch parameter (where 'x' is the desired framerate cap, such as 144 or 240 fps for high refresh rate monitors).
Many lighting issues have been fixed. As a result, lighting should look smoother.
Re-enabled some missing effects on the "Axe" weapon model.
Added new text/warning messages when a player attempts to insert an item other than a teleporter piece into the standing stones, or attempts to cook meat on an unlit fire, or attempts to put an item in their inventory that they do not have room for.
Upgraded the navigation backend to the newest version.
Fixed a bug where it was possible to open the menu while the screen is still fading in (pauzing the fade-in, resulting in a black screen).
Added a button on the class selection screen that allows players to return to the main menu.
Fixed a bug that caused docks to spawn on inland lakes instead of on the coast.
Fixed a bug that caused docks to spawn in the corner of the map, outside of the playable area.
Fixed a bug where teleporter pieces would spawn inside of other objects, partially obscuring it or making it inaccessible.
Fixed a bug that caused the "Dog" models on the main menu to not animate.
Fixed a bug where it was possible to be shot at, and killed during the ending cutscene.
Fixed a bug where dogs could perform their "bite" attack through walls.
Fixed a bug where weapon models would remain visible (and respond to mouse movement) after the player dies.
Fixed a bug where it was possible for toy trains to ride across the water (toy trains now explode when hitting water).
Fixed Z-Fighting issues on certain building models.
Fixed a bug where the Rider NPC, and certain objects in the "industrial" biome would render fog incorrectly.
Fixed an issue where Ambient Occlusion would render incorrectly during the ending cutscene, and on underwater objects.