Optimal is correct, variegated F. elastica, I like its variegation, handsome. You could try the Houseplant Forum & search there for this plant, by both names to find care info to read.

LatinLady Yes, there was a rot along the stem from the inside, actually in Spring of that year it showed very tiny leaves, then those leaves dropped before opening or growing more, and then I noticed the dark brown and squishy part of the stem from the bottom. I didn't water it on winter and was covering its pot and the top of the soil with a cloth, though I really don't know what I did wrong, but probably it was sick already when I bought it? because there was a big light brown spot on the stem, and it didn't flower. Actually I talked about this in other posts too: https://www.houzz.com/discussions/5357202/plumeria-is-awake-but-not-growing https://www.houzz.com/discussions/5032149/slightly-soft-or-squishy-plumeria-stem https://www.houzz.com/discussions/4976037/advices-about-careing-for-and-overwintering-dormant-plumeria https://www.houzz.com/discussions/5507561/help-with-black-tip-fungus Thanks again, and all the best to you too :)

2. Mammillaria - Someone here will be able to ID it further after it blooms. Please repost a picture then. 7. Gymnocalycium mounted onto hylocereus ... Same as above for further ID applies. The purplish and green ones root and live on their own. They have chlorophyll and do not need to be mounted onto root stock. They can take a very long time to root and can live years without them but won't thrive if they don't. It's the yellow, orange, and red ones that need grafting onto a host plant. I had an orange one that gave off tons of pups and lived 19 years. I used it to learn to graft my own "Moon Cactus" and actually gave away about 12 from that one plant ... until I tried to ship it to myself during a move. Thanks USPS for beheading my lovely friend. These are full sun cacti if you want to see blooms after they turn about age 3. Maria Elena

Amaryllis bulbs need to be partially exposed to grow well.