[RPG] find the “Trap the Soul” 8th-level wizard spell

I would say no to both copying and casting Wizard spells above level 1, based on the spellcasting rules under multiclassing on pg 164 of the PHB:

You determine what spells you know and can prepare for each class individually, as if you were a single-classed member of that class

I read that as saying that you would count as a level 1 wizard, which comes into play under the and can prepare section. A level 1 wizard cannot prepare spells higher than first level. Nor would they be able to scribe them, as spells you are allowed to know are also based on individual single class.

PHB Example with wizard on pg 164 as well:

As a 3rd level wizard, you know three wizard cantrips, and your spellbook contains ten wizards spells, two of which can be 2nd level

The first errata to the PHB clarifies this explicitly:

Your Spellbook (p. 114). The spells copied into a spellbook must be of a spell level the wizard can prepare.

But, you would be able to cast a level 1 wizard spell as a 9th level spell slot, per PHB rules further below:

If you have more than one spellcasting class, this table might give you spell slots of a level that is higher than the spells you know or can prepare. You can use those slots, but only to cast your lower level spells. If a lower level spell that you cast, like burning hands, has an enhanced effect when cast using a higher-level slot, you can use the enhanced effect, even though you don't have any spells of that higher level.

Short answer: Yes. A soul consumed in a phylactery avoids any afterlife, and once destroyed after 24 hours it is gone completely.

With the religious structure in Forgotten Realms, any type of afterlife is depending on the Deity the character worships. To the point that if the character does not worship any kind of Deity in the Forgotten Realms setting, then divine spells to bring the character back from the dead are not effective, and the character's soul is supposed to sit in a kind of limbo for the rest of existence.

Also, the Imprisonment spell traps both body and soul, so it's better to think of the character being transported to another realm. With both body and soul intact and still connected, the character should still have awareness of their surroundings. In this case, their existence is now inside the Lich's phylactery.

There is no source that describes any specifics about what a creature experiences inside a phylactery. Whatever the character perceives in there is up to the creativity of the DM and the player.

However, since the soul has to be free to be delivered to their Deity to experience an afterlife, the character wouldn't experience that. While in the phylactery, the character doesn't experience an afterlife. After that 24 hour period, the soul is destroyed, not transported to their deity to experience an afterlife.