

Veracrypt has back-up headers located elsewhere in the volume that are unlikely to have been overwritten.
First thing’s first I would strongly recommend copying the drive as it currently exists bit for bit to another drive of equal or larger size. Don’t work on the original if you can help it.
Now with this copy, you should try to check the option to use the backup header when mounting and try again. If the partition is gone and veracrypt doesn’t see it you’ll need to try using something that recovers partitions and doesn’t mind encrypted partitions or partitions or file system types it doesn’t understand and use that to ON THE COPY recover and recreate the partition (this will write data and can cause the possibility of further loss or worsen your ability to recover which is why it is important to perform it on a copy). Testdesk may work for this but there are other options that probably are better.
See this list: https://old.reddit.com/r/datarecovery/wiki/software and choose something from there if this data is truly important. Again only work on a copy on another drive. Some of these software examples actually work against the original drive and make a copy elsewhere and should be safe to use on the original drive so long as they have you select a target drive to push the recovered data to but read the documentation. Testdisk absolutely must be used on a copy.
You will incur data loss and likely should run one of the file recovery software mentioned on the drive once successfully mounted in veracrypt to attempt to recover as much as possible.
Not even a choice.
If you choose over 100F you will see electronics failing more often, working harder, less efficient, working badly, etc because the heat is causing them to throttle in various ways. In the modern world it is far, far easier to heat up a space with a house full of electronics and humans than it is to keep it cool. The energy required to raise the temperature from say 5 degrees F to a more comfortable 40 degrees (35 degree change) pales in comparison to the energy required to keep yourself and your devices cool a mere 10-15 degrees less to around 90 degrees which is still uncomfortably hot and sweaty.
I’ll note that a constant 100 degrees is more than hot enough to cause various foods, medications, substances to break down and go bad. Check your medicine cabinet, most of your pills including over the counter are only rated for storage at up to 86 degrees. Your medicine will lose efficiency or go bad in some, perhaps many cases. Your food outside your fridge will spoil more quickly, mold and bacteria will grow more quickly and readily. Your fridge itself will work harder and die sooner.
The tap water will run hot or warm most of the time meaning a shower won’t necessarily cool you off much.
The colder temperatures are cheaper all costs considered, feel better, can be negated at a moment’s notice with socks, a jacket, and a blanket.
It’s easy to insulate a home against extreme cold and just retain heat you generate inside including by your body and devices. It requires a lot more effort to keep the inside cold when both the outside and things inside are generating heat and trying to warm it up.
This is a reason why climate change is a nightmare not just for human comfort but on so many levels. Our electronics are going to operate less efficiently in a warmer world and draw more power to do so.