Ok sorry.
Yes sac305 is a common lead-free solder. It's not easy to replicate the properties of lead-tin alloy, so there are a lot of different alternatives and none of them really work quite as well.
There's 2 classes of problem: usability and functionality.
Lead-free is both a little more difficult to use, and then is a little more likely to fail over time.
Usability:
The usability problems are 2 things, higher temperature, and surface finish.
In the best case with old lead-tin, you still have to develop a skill to get in and get out relatively quickly and not keep the heat on for a long time. Even the relatively lower old temperatures are still hot enough to destroy most components and the pcb traces if you lay the heat on for extended times.
But all of the lead-free alternatives require a little bit higher temperature, and so there is a smaller window of time to goof off and blunder around with the heat on. Smaller but still easy enough. A datasheet for a component might say something like max 300c for 3 seconds, but really you can poke around for 30 seconds at 350. 30 seconds is forever. If you can't get it done by then, the problem isn't the solder.
The surface finish matters because in the old days it just so happened that you could be a cave man and still know if you made a good joint or not simply by the surface finish. If it's shiny, it's good (probably), if it's dull, it's bad. sac305 usually cools to a dull finish even if everything is perfect. You can still tell if you made a good or bad joint, it's just not as utterly black/white simple as before.
Both of those are just, it's a little more difficult. Still perfectly doable and not just by some wizards and not by most mortal humans.
Funcionality:
The most valid problem is the performance, where after doing the sufccessful soldering, the solder fails in some way later on.
sac305 and most others are generally a little less ductile and prone to crystalization and fatigue cracking, and the biggest problem is tin whiskers.
sac305 is pretty much the worst for growing tin whiskers. On fine-pitch legs on surface mount parts the pins are close enough together that in bad enough environmental conditions, whiskers can grow to short between two pins eventually.
But, it takes particular conditions and doesn't usually happen to most ordinary things kept in ordinary indoor environments, and if you're building something that has fine pitch parts and you know it will be used on a boat or something you can mitigate that by adding a coating, and lastly in this case, point-to-point wiring in an antique radio is way too large to have any tin whisker problem. Whiskers grow to something like 500um in the worst case. It takes both a bad environment (presumably and "antique radio" will be protected and not used on the deck of a saltwater fishing boat) and requires parts that are almost touching each other. Antique radios don't even have PCB's. Medium-old electronics that havs pcbs but through-hole parts are maybe barely subject to whiskers. It will be uncommon for a whisker to reach all the way between 0.1" (2.54mm) chip legs, but not impossible.
These things are certainly problems. That's true. Yet it's also true that most electronics have been using nothing but this stuff for almost 20 years already by now.
There has been exceptions allowed for specialized things where the functionality and performance of the lead alloys was necessary enough to outweigh the environmental impact. But they are about to remove a lot of those exceptions soon. It is a problem, but it's not a problem for any hobbyist.
This subthread, my reaction, was exactly about the suggestion about "some retro guy repairing an antique radio". That guy absolutely not even close has any need for lead solder, and yes, that one guy using it does poison the environment, because there is no such thing as one guy. It's countless guys. If one guy can buy and then use something, then so can everyone else. And for every one of those users, theyr aren't just soldering a few joints one time. They have 1lb spools of solder and ALL of that solder eventually winds up in the ground and leeching into the water and soil. Most of it actually gets turned into fine dust because that's what happens when you clean the tip, which you have to do continuously, and when you desolder something, the vacuum atomizes the liquid solder as it's being sucked out of the via.
That's why it's so bad. There's no such thing as just one guy doing it, and for every one of the people, imagine taking a pound or two of lead (solder isn't 100% lead, but a single person will posess a few pounds or more total of different solders) and imagine say 10% of that lead being actually in some project. Then another say 30% being in the form of little bits and pebbles and the size of a bb and discarded joints like bits of soldered wiring cut off and discarded, and the rest, say 60% all in the form of particles the size of sand all the way doewn to very fine dust. And all of that solid pound of finely ground pebbles, sand, dust, ends up just everywhere, only some ends up in the local dump. a lot ends up just in the structure of the house and the ground under and around it right near wherever the work bench is. When you sweep and vacuum your work area, you are not remotely actually recovering all that lead dust.
And the next family to occupy that land didn't sign up for that.
When I say "no excuse" I mean that, there is no overriding need that justifies it. Sure lead-tin works better both while using it and then klater for the life of the object, but it doesn't work better enough, and for most people the application isn't critical enough, for that to outweigh working towards the goal getting led out of the environment.
Unleaded gasoline is way more difficult to use and less performant and has cost everyone billions, and we all shouldered that burden, only so that some man-baby can undo that very difficult and costly work just so they can solder a wire in a radio a teeny little bit easier?
No. The two considerations don't compare at all. It's just that one is easy to see and one is not so easy to see. One you can see with your eyes right now and gives you immediate gratification, and one you have to see with your mind, and you have to care about anything but your own convenience as the single most important consideration above all others.