I hit this problem on my 1-year-old Mac Mini which is running macOS Catalina version 10.15.7 (19H524). It happened after a system-crash, but probably more importantly after that system crash I upgraded Xcode to Version 12.4 (12D4e) via the Mac App store. The crash happened on my main userid (local to this Mac), but not on a different userid on this same Mac where I rarely run Xcode. I tried several of the suggestions here. I emptied the "Open Recent" menu (and it was indeed empty the next time I ran Xcode), but Xcode still crashed. I tried using the open command to edit a source file in Xcode (this is something I do very often), and Xcode still crashed. I opened a few different source files this way, although none of them were for Swift source. I also used the defaults command at the unix command line to delete many of the defaults which were set in domain com.apple.dt.Xcode. I didn't delete all of them because I didn't want to have to reset my configuration for Xcode. Removing those defaults-values did not stop the crashes. I then downloaded the developer-example files of 'Swift Standard Library.playground' and 'Crustacean.playground'. I double-clicked on the SwiftStandardLibrary file, which caused Xcode to launch. That example playground did some of it's own initialization stuff, and once it was done Xcode was still running. I closed the playground, went to edit the files I normally edit with Xcode, and everything seems to be working fine. I have not had any crashes since then. I am not 100% sure, but I'm pretty sure that I have never worked with a Xcode playground on this userid on this Mac. I'll also say that I use Xcode as an editor for my own source files. Which is to say, I am never using Xcode projects (not on this mac, at least. This mac is only used for me "working from home" on my full-time job, not for Mac development. That's why the Mac is 1-year old...). I have filed a bug report with via Feedback, and included some crash-dumps from when Xcode was crashing. So hopefully that will help Apple find and fix whatever the bug is.