It is a reddish flag
Old an worn wisdom about interviews being a two-way street applies here. As others pointed out, internships are usually a low priority, it takes time to arrange a meeting, it is a holiday season, COVID-19 complicates everything etc ... But, where that leaves you ?
Let's us suppose you continue process with this company and they hire you. Primary purpose of internship is to learn. And it looks like your company actually does not know what would they do with interns. Sure, they certainly want to have some, after all other companies are doing it, cooperation with academia, maybe even some tax breaks etc ... But at the end of the day, they are either too busy or too inert to bother with you. You will sign up, and then you will wait another two weeks to actually get something to do, then they would forget about it and you would have to pull their sleeves to gain some attention etc ...
If you are looking simply to formally complete internship (requirement for you university course or something), plus make some money on the side, I would say you could give it a try. You would actually probably have a lot of free time on the "job" and you could use it to study or pursue other interests . But if you want to actually learn something, try to find smaller company with tighter budget (maybe even startup). They would usually hire junior developers and try to work them as hard as they could, which in this case could suit you fine because you would be able to gain lot of experience in a very short time. As always, choice is yours.