Hello there tihorog386 and welcome!
Some of the games I would recommend for female weight gain on the site are: (just click on the summary drop down arrow to expand)
Click here for drop down game list
@tiggertoo’s The Weighting Game - 3d visual novel using daz 3d renders and renpy. It’s a WIP so more to come in the future. You play as a male MC with plenty of female weight gain.
@Roops The Breakfast Chub - 2d visual novel game that was made for the 2019 Fat Fortnight game jam. This version is complete. It’s a short but sweet game where you play as a new hire at the Sweet Spot Cafe and work along side your new trainer and co-worker Claire. And as you would imagine weight gain ensues.
Roops also has another game still in development Feed the Crown: Deluxe Edition based on their submission Feed the Crown for the 2020 Gain Jam. The Game is a 2d platformer that has you taking the role of a knight trying to collect and steal food from the Pig Kingdom. You can use collected food on one of the three different queens you choose to serve in the beginning. After a completed (or not) run you are rewarded with a dinner scene with your selected queen and the food you have collected.
@SirKata’s and @hisano-x’s Comfy Campanion 2.0 demo - 2d visual novel where you play as a main character that works as a social media influencer who is also a feeder. Your friend gets you roped into a situation with a new model/pet (able to choose between one of two) either male or female kitsune name Lapis or Ruby. This is based off of Cakecatboy’s 2019 Fat Fortnight game jam submission. Comfy Companion. The 2.0 does continue from the original so I would advise playing cake’s version first. 2.0 is still a WIP with updates to come at a later date.
@Tron and Team spoon’s Forks: A Weight Gain Visual Novel. - 2d visual novel using renpy (later to be unity) where you play as a female protaganist Alex as she attends college looking to balence her personal relationships and wants within her life. She is interested in weight gain but been scared to ever commit fully early in her life once she starts to gain weight. There are a lot of girls in game and it is set to take place over the course of four years. There is a demo on the first post but also a unfinished teaser demo here. Be warned the demo is missing art, sprites, and some changes that are to be finalized with an official release of the completed 2nd demo later. I would wait on this the 2nd demo if you would like to wait for the more completed version.
@mythical-chikin’s Unfulfilling Isekai Simulator and NPC Simulator. Both games are 2d rpgmaker games with sprite work done by CJ-X4. In both games you play as an NPC that fattens up adventurers. Both are great, Unfulfilling Isekai Simulator was originally going to be a sequel but that changed. So, play one or both, either order is fine. Npc sim is finished and the other is a WIP.
@LazerCamel’s and again Cj-x4.3’s Fattaker - remake of the original Helltaker on Steam (steampowered.com) with fat and some weight gain. This version is complete but they are working on another one that has at least one more weight stage beyond the current game.
@eltipito42’s Thicker Treat: A WG Dating Sim - 3d using daz 3d and renpy dating sim where you play as main character that can romance and date from a wide cast of female characters there is a free 1.0 Alpha release here. With a 2.0 just released for patreons. The game is a WIP.
moonslashx’s Surviving, a WG and Expansion Game - 3d daz render game using Rpgmaker set in a post apocalyptic setting, you play as a male MC in a world with a murderous robot uprising has taken place and you and a (much smarter) female scientist live in a compound where you are just trying to survive. Multiple girls, with weight gain, BE, AE, etc. within the game.
@wholehog919’s Whole Hog -3d visual novel using daz and renpy. You play as a male MC that is a feeder and has recently broken up with his girlfriend. Getting a job offer, the MC takes it looking for a new fresh start. You run into and date a girl at your new apartment named Danielle and good stuff ensues. The game is a WIP.
WaxeRed’s Apostles - 2d rpgmaker game with a great world building and characters. It’s a bit of a slow start for the first hour (as far as weight gain content goes). It’s definitely worth hanging around for in my opinion. You play as three different main characters who are missionaries looking to spread the word of the three Niss, Gulia, Luxuria, and Acedia. You come across a town that is rundown and starved. Looking for a push back into the right direction, and maybe a little further.
fallboy3656622’s Feeder Fantasy (original Japanese version) - 2d rpgmaker game with great visuals by Sunny3257_29. There is a link to an English translated and modifed version for 5.0 by StygianSkies here. You play as a Male (modifed version is Female) MC that is a feeder and looking to go around and fatten up female heroes and other female townsfolk. The MC can gain weight in both versions as well.
humblesasquatch’s The Next Big Thing - 2d rpgmaker rhythm based game. Where you follow Amy and Emily who enroll in an academy for belly-idols.
juan_alvarez’s Hungry Elves with the English translation here by Erronwolf. 2d rpgmaker game. You go around as a male MC who is a feeder, that finds themselves stuck fighting against demons, monsters, and servants. With the help of a trio of elves, his human neighbor, a catgirl, and more. The game is complete. (Erronwolf and team are also working on Eternalland if you find yourself likely hungry elves.
Just to name a few 
. Honorable mention to @vrazz’s The Queendom of Corpula (formerly The Kingdom of Corupula) if there was still a demo up I would recommend this one as well. It is back to being a WIP and hopefully a new demo for that the game sometime here in the future.
There are a ton of good things for both male and female WG on the site and there is also a user-maintained list of games. It has alot of games on there but know that there are a ton more not added to it.