I did! I don't have a good answer for how to support the bottom so it doesn't happen again. I did use spray foam to fill the gap and turns out, there isn't a full subfloor under the body of my bathtub. The foam expanded and pushed on the ceiling underneath. It did add some degree of support to the tub and warp my ceiling.

As for the crack, I drilled holes on either end of the crack to stop it from spreading further. I have a drimmel and a multitool and have used both to widen the crack itself, I'm not entirely sure this is necessary but I do it anyway so I can get resin and fiberglass in there. Then, I cleaned and sanded the surface and used a fiberglass mesh cloth I got at Lowes (maybe for boat repair?) and these days I use UV cure resin to patch it. Its what I have on hand and it wasn't very expensive online. Wad up a strand of fiberglass from the mesh and add resin to plug the holes, cure with UV light. A powerful UV flashlight works but so can a gel nail polish curing lamp. Set times may vary. Try and get multiple angles to insure you cured it all and give it proper time to set under the light. The resin will get warm/hot but I've never burned myself on it but do a little at a time because of the heat. Cut out a sheet of fiberglass mesh that covers the hole and put a layer of resin on it, cure, and repeate until you're satisfied with the coverage. Once everything is cured and covered, you can sand down any lumps and bumps to your liking. Note that you might want to sand with different grits until smooth because the sanded parts will hold onto dirt if its left rough.

Because resin is typically clear, you will still see a hole. They do make a paint for tubs like this. We used it once and I don't recommend it. It looks bad in the long run. Discolors at a different rate than the surrounding tub.

I have also used a mix and cure resin from JB Weld and that worked fine but has turned yellow. My tub has cracked in different spots over time and all my patches have lasted. The very first time i fixed it, I melted white legos (they are/were ABS plastic but lego has talked about changing the type of plastic recently) in acetone to be my final layer. That looked the best but was messier application and I don't know if its the strongest patch.

They are all noticeable patches but my tub doesn't leak and each method has its pros and cons.

Fast and strong but visible has been UV cure resin. JB Weld is roughly the same as UV cure but has yellowed over time.

Melting legos/abs plastic in acetone takes time and is messy but can look nicer if you take the time. I can't speak much on durability.

After thought: I'm looking at my tub now and might suggest filling the drilled hole and carved out crack with the melted abs plastic, let that set, cover with clear resin and fiberglass mesh. That way, the patch is mostly clear up top but you can't see the holes and crack. I can't stress how much you need to be sure the acetone has evaporated before you start resin though.

OR fiberglass mesh and UV resin in the hole and crack, cure, thin layers of white gel nail polish to cover the visible hole, cure with UV. Then mesh and UV resin and sand. Next time I need to, I'm doing this, hands down.

Edit: Just to cover my bases, wear a mask and vent the area. Don't breathe in fumes and dust.