Someone tried to steal this bike - they damaged the top tube. The frame is designed with a wide flat top tube. Is this still safe to use?
My opinion, which is very much my own, is that this is safe to ride home and may provide some level of “emergency use” where no other bike is available and you need to get around for a short while, but realistically the frame is at End Of Life now, the structural integrity is severely compromised and the long term reliability is deeply uncertain.
Replace the frame as soon as funds allow.
I’m not an engineer. With that caveat, I think this frame is likely to fail. It may depend on how thick the tubing is, and if you see little cracks anywhere on the tube, I would stop immediately.
Anyway, you now have a serious dent in the tube. All the forces on the frame, like hitting a bump, riding out of the saddle, etc, are now flexing that area. Chances are there are already some micro-fractures there, and they will propagate with load. That will eventually crack the tube through.
Personally, I would replace the frame. With steel, in principle, dents may be rolled out if the tube isn’t cracked, although that’s a big dent. You’d consult a framebuilder for that. Aluminum doesn’t repair in that fashion due to metallurgical properties.
I would ride that bike as little as possible before replacing it. Being aluminium, it will fail rapidly once the metal tears properly. If it were steel with the same damage, it could still outlast us with that dent.
Can you claim insurance on it? Get your LBS to state it is unsafe to ride as a result of attempted theft, and make a claim.
There is no repair for aluminium bikes, because welding would require heat-treating to restore the temper. This is unfeasable for a complete frame because of costs.
Your best bet is to treat it as a donor bike of parts, and try to source a replacement frame or a complete bike that has wear then combine the two.
Finally, consider how you can protect your bike better in the future. That level of locking in that location was insufficient to deter thieves, so you need to make your bike less-attractive. Add more locks, make it less appealing, or even park it elsewhere (inside). Good luck !