>Lack of ultrawide 21:9 resolutions in the ingame settings<
This is an easy one. Open the Sam2.ini located in:
C:\Program Files (x86)\Steam\steamapps\common\Serious Sam 2\Content\SeriousSam2
And then look for the lines, gfx_pixResWidth = X; and gfx_pixResHeight = X;
Change the X value to whatever screen resolution you have such as 2560x1080. No other ini edits are needed. After this the ultrawide aspect ratio works almost perfect since the game was optimized by the devs already for this.

>Object and grass view distance pop in<
Ever noticed how objects and grass suddenly pops in right in front of you and you would like to fix it? Nothing easier than that. Go into your Sam2.ini again and look for "ren_fLODBias = X;" and "crm_fDistanceBias = X;". Change the first value to 0.1 and the second to 5. After this the object and grass pop in will be gone.

>No FOV slider setting ingame<
The game supports FOV changing but only via ini edit. Go again into the ini and add the line "plr_fFOVOverride = 93;" to the bottom. This one isn't in the ini by default, you have to add it yourself. You ALSO have to right click the Sam2.ini and click on properties and make it READ-ONLY. Because the game removes all player added lines such as these which means after each restart the change would be gone. You can change it to whatever value you want. I found 93 perfect for my 21:9 aspect ratio but feel free to try around.

>Any ways to use antialiasing methods such as SSAA or SGSSAA?<
YES! I actually found a fix for Nvidia Inspector that makes it possible to use custom anti aliasing again. For some reason without a fixed compatibility ID, the AA driver options do not work anymore. I think this might be a Windows update problem but no idea. Go into Nvidia Inspector and use the compatibility ID "0x004412C1". After this change the antialiasing mode to override and the setting to for example 8xSQ or whatever you want. I usually always go with 8xSQ since it looks great and isn't too overkill on the performance. No more aliasing!

>21:9 FOV - Klodovik bomb weapon FOV fix and see more of your weapons<
I noticed that at least on ultrawide the arm of the Klodovik weapon is clipping. I am not sure if this is a issue for everyone but I doubt it. Then again originally the FOV was only designed for 4:3 aspect ratio anyway. It looks a bit too much zoomed in for my taste too. I made a 21:9 weapon FOV mod for this. This fixes all clipping problems and also makes you see more of the weapons without looking odd or over the top. This mod ONLY works on 21:9 ultrawide screens and will look bad anywhere else.

Download for the 21:9 FOV mod: httpsX/www.mediafire.com/file/vjif53zx89ponz4/Serious_Sam_2_-_Ultrawide_Weapon_FOV_Improvement_Mod.zip/file
Change the "X" behind https to a ":"

Just copy the downloaded files into the main game folder. The folder structure is already given so it should be self explanatory. If you do not like my weapon FOV model changes, feel free to use only the KlodovikGunWeaponRendering.ep since that fixes the arm glitch. All the other FOV changes I made so that I can see a bit more of the gun since I found some of them way too close to the view.

Before my fixes:

After my fixes: