I've been using version 1.12.2 of Forge. It's been a few months, so I don't really remember exactly what I did, but Forge updated to 1.13. Now, I can't use any of my mods; all are for 1.12.2. I've tried redownloading and reinstalling 1.12.2, but it doesn't work. What should I do?
Separate your mods by version number folders in your .minecraft so if you want to play 1.12.2 mods put them into a 1.12.2 folder, change to the 1.12.2 Forge profile and run the game to play those 1.12.2 mods. 1.13+ however you can't run mods in an folder deeper like with 1.12.2 and prior versions of Forge so you have to run any mods for Forge 1.13 and 1.14 in your mods folder.
Just remember that 1.12.2 mods only support 1.12.2, not 1.12 (sometimes) not 1.13.2, not 1.7.10, only 1.12.2 so you'll need to get 1.13.2 mods, and if the mods you want aren't ported to 1.13.2 yet you'll just have to stay on 1.12.2 with them or find new mods or use a few that have been ported. I do it all the time and it can be fun to learn new mods or work around limitations but I know that's not for everyone.
Separate your mods with folders like so if you have to, I have a lot of mod loaders between 1.13 and 1.14 so you can tell I use these a lot, but even for those modloaders (Rift and Fabric) you have to take them in and out of the folder their in and put them into the mods folder not try running them in the 1.14.4 (that I use for Fabric) or otherwise because only Forge 1.12.2 and prior allows for running in deeper folders.
This solution makes things a lot easier, if it gets awkward though you can always use Twitch Launcher to make profile and mod instances easier.