What can be done with old (unprofitable) ASICs? GPUs used for bitcoin mining have many other purposes and can generally be sold after they are no longer mining enough Bitcoin to meet variable (electricity, etc) costs.

What uses do old ASICs have after they are no longer profitable to operate?
If your electricity costs are high, unprofitable for you may mean profitable for someone else.

Some miners may still use unprofitable ASICs either to support the network (at a smaller loss than with GPUs) or in hopes that BTC price will rise in the future (although just buying BTC in this case may be more profitable).

Try to sell them. If you have no success, then recycle them or use them as weights, benches, etc.