Is it normal for SolidWorks to show ads on the loading screen now?

Nope, no setting for it as far as I can tell. I went through System Options twice, checked under both Display and General, and there's no toggle for the promo content specifically. It's baked into the welcome screen now, and the actual ad content gets pulled down from thier servers when you launch, so it can change without you ever seeing an update install. That's why it caught you off guard, nothing on your end actually changed except what their server decided to serve that morning. The closest thing to a fix is killing the welcome screen entirely. There's a little gear icon in the corner of that dialog, and one of the options is wether it shows at startup. Uncheck that and you go straight into the app clean. Trade-off is you also lose the recent documents list on launch, so it depends how much you use that. I got in the habit of pinning my active projects to the taskbar anyway, so I don't miss it.

What I haven't tested is whether blocking the ad domains in the hosts file blanks out the banner while keeping the rest of the screen. Someone on the forums mentioned trying that route, and since the content is network-served it seems plausible, but I can't confirm it works or whether it just leaves an empty box. Might be worth experimenting if you want the welcome screen back. And yeah, your instinct about the slippery slope is fair. This started on the maker licenses first, then rolled out to the paid tiers, wich tells you they're testing tolerance rather than targeting hobbyists. Filing it through the customer feedback channel is about all you can do beyond the workaround. enugh subscription holders complaining is historically the only thing that's gotten them to walk back UI garbage.

I can confirm the hosts file thing at least half works. I blocked the domain the welcome dialog pulls from on my machine and the banner area now renders as an empty gray strip instead of an ad, with the rest of the screen behaving normally, so the frame itself is local and only the content is remote. Whether an empty strip is better than an advertisement is a matter of taste, but I prefer it. One thing I noticed while testing: if I launch with the network cable unplugged, the whole welcome window loads faster and falls back to a plain state, which suggests the ad fetch is blocking the startup sequence a bit too. I have not timed it properly, so treat that as anecdotal.

The gray strip thing matches what I saw too, only mine didn't stay empty. A couple weeks after blocking the domain an update quietly added a second one and the ad came back untill I spotted it in the hosts file and blocked that as well. So if anyone goes this route, check it again after each service pack because they clearly rotate the source. I also shrank the welcome dialog down to nearly nothing so the strip is barely there, and I keep my current job files in the recent list at the top of the File menu anyway, so losing the launch list never bothered me.