Searched most popular mods on Curseforge (about 30 pages worth, found a few good recommendations for the server if the server op wishes, and no, none of these will break your server install, just check and double check all your configs)
https://minecraft.curseforge.com/mc-mods?filter-game-version=1738749986%3A628&filter-sort=4
ComputerCraft - mod that’s all about computer programming. Allows you to build in-game Computers and Turtle Robots, and write programs for them using the Lua programming language. Various turtles including a mining turtle which will tunnel mine or quarry mine. Some built in programs, be sure to read the wiki. It is also OPEN SOURCE http://www.computercraft.info/ ,
https://minecraft.curseforge.com/projects/computercraft
NetherPortalFix, this mod fixes the multiplayer server issue with Nether Portals https://minecraft.curseforge.com/projects/netherportalfix
Backpacks, allows more player inventory storage space and naming (Tool Bag, Blocks Bag, Food Bag, etc.) https://minecraft.curseforge.com/projects/forge-backpacks
Journey Map, needed client and server side, allows mini map and waypoint markers, only opped players can teleport https://minecraft.curseforge.com/projects/journeymap
Hammer Time! Allows vanilla versions of Tinkers Construct hammers (that mine 3x3 blocks at once for tunnel mining) , spades, lumber axes, and sickles, great for small packs that do not include Tinkers
https://minecraft.curseforge.com/projects/hammer-time
Iron chests, allows bigger chests in 1 block https://minecraft.curseforge.com/projects/iron-chests
Chest Transporter , allows you pick up a chest with its items and place it somewhere else (like the dolly from Open Blocks mod) https://minecraft.curseforge.com/projects/chest-transporter
Inventory Sorter, allows 1 button click sorting of opened chests by ID number or mod item for stacking to save space, amongst other useful things etc. (replacement for Inventory Tweaks mod) https://minecraft.curseforge.com/projects/inventory-sorter
OpenBlocks Elevator, block that when stood on top of, and spacebar activated transports player upwards up to 8 blocks to another Elevator block, when L shift (sneak) activated transports player downward up to 8 blocks to another Elevator block
https://minecraft.curseforge.com/projects/openblocks-elevator
Open Glider, adds a hang glider
https://minecraft.curseforge.com/projects/open-glider
Morpheus, good for servers in that it allows (in config set to 1%) 1 person sleeping in bed to change from night to day
https://minecraft.curseforge.com/projects/morpheus
Neat , adds mob health bar similar to RPG games
https://minecraft.curseforge.com/projects/neat
LagGoggles , profiler where you can see timings in the world, visually. It comes with a custom GUI using a configurable keybind
https://minecraft.curseforge.com/projects/laggoggles
VanillaFix , useful for server ops, not necessary but has some nice features and worth a look https://minecraft.curseforge.com/projects/vanillafix
Fullscreen Windowed (Borderless) for Minecraft, allows numpad selection of preset resolutions, read info.
https://minecraft.curseforge.com/projects/fullscreen-windowed-borderless-for-minecraft
Optifine is great for lower end computers struggling with bad performance / fps , allows much more control over video and rendering options, resource pack supported, install the proper version for the Forge version you are using
https://www.optifine.net/home
Official mod supported Faithful 32x resource pack (Forge loads only the modded textures for the mods you are loading no matter what modpack, so it is very lean with small packs, increase your launcher’s Java allocation to 4-6 GB maximum for best results) it is universal and community supported
http://www.f32.me/
I highly recommend using Multi MC for client loading (it is very very lean compared to Twitch app and other launchers and is what we modpack devs primarily use to make modpacks) , it has many extra options such as extended console logging and use of profilers etc. , very simple to use for beginners and powerful enough for advanced users, also allows drag and drop importing and exporting of modpack zip files (useful for easy pack distribution / download if you are running a community server). https://multimc.org/
