Also it's important to know what "unsupported" actually means in this context. It means that .NET 7 won't be updated further, including to fix security vulnerabilities. That doesn't mean .NET 7 is "immediately toxic". It's fine until there's a newly discovered security vulnerability that isn't fixed which then necessitates migration to .NET 8+.
And, since Paint.NET uses SCD (self-contained deployment), you really need to consider the scope and meaning of "supported"/"unsupported". Microsoft does not "support" Paint.NET. I do, this forum does. If there was a security vulnerability in .NET 7 that was important to Paint.NET, and 5.1 wasn't ready yet, then yes I would push forward with a 5.0.14-on-.NET 8 release. Unless that happens, just chill and wait for PDN 5.1 on .NET 8 which is already coming soon.
PDN isn't enterprise software with an SLA or a support contract (although if you need that then we can talk). As such, you need to temper your support expectations. I do take security very seriously, I learned a lot of this mentality at Microsoft in the mid-to-late 2000s, but unless I'm being paid for it you can't expect me to drop everything and change course just because .NET 7 transitions to "unsupported" status. It's fine to have a gap if there's not actually a security vulnerability to worry about. (I'm not making the assumption that you were being aggressive/entitled, I'm just making things clear)