Some mods I would recommend to combine with RTX Remix. Make sure to use the custom Fusion Fix fork that comes with RTX Remix, so you can install all of the recommended mods with the modloader from Fusion Fix.

Game Mods:
Project Lights: https://discord.gg/g26nxTQpNp
Light source overhaul mod for over 400 models all around the map.

VariousFixes: https://github.com/valentyn-l/GTAIV.EFLC.Various.Fixes/releases
Huge mod with thousands of improvements and fixes for basically everything.

For the two mods from above, make sure you have the same load order as you can see in the "Update Folder Load Order.png" picture.


RTX Remix Mods:
AutoPBR: https://github.com/xoxor4d/gta4-rtx-autopbr-mod
A huge pbr materials texture pack for several vanilla textures.

Kaba 4K PBR Roads: https://www.nexusmods.com/gta4/mods/949
Higher resolution road/ground surface textures with custom pbr materials made for RTX Remix.

Kapibos 4K High-poly model set: https://www.moddb.com/mods/kapibos-4k-high-poly-model-set-rtx-remix/downloads/kapibos-4k-high-poly-model-set-rtx-remix
A huge set of 4K high-poly models made for RTX Remix.


Warning:
Don't use any of the recommended mods from the usual "Recommended Mods" folder outside the "RTX Remix Version" folder. Only the ones from the "Recommended Mods" folder that you can find here in the RTX Remix version are compatible with RTX Remix.