Welcome! Your window looks great!!! The rest of the Sans looks good........the way the spot is in the middle of the leaf suggest there was some damage to that leaf at some point (probably before you bought it) and/or infection on that leaf only. I typically get some damage like that over winter anyway after bringing my Sans back indoors. If the damaged area is fairly dry I would not worry. If it is damp/soft and/or if it looks like it is spreading on the leaf then cut the whole leaf off at the bottom of the leaf, well below the spot, close to where the leaf meets the stem. The rest of the plant should be fine. The pot looks plenty big enough for the time being, though the soil does not look great. I would get a bag of cactus soil and a bag of perlite and mix them about equally. Knock off most of the old potting soil from the roots (you don't need to get every last bit) and replant in the new soil.....and water it in. Oops I just noticed you have soil. I am not familiar with the Bonsai Jack but that mixed with the other would probably be fine........but I would probably add some extra perlite too for aeration and drainage.

You say you water once a week.........there is no calendar time that is right or wrong for watering. Feel the soil (or insert a wooden dowl into the pot). When it is dry it is tiem to water again. Plants will use more water and need watering more often in the spring and summer when actively growning and the days are longer and temperature warmer, less when dark and cool and off season (like winter). If two plants are in the same size pot but one is much larger the larger one will probably need watering more often than the smaller one. A plant in more sun and perhaps with a fan on it is going to dry out quicker than one that is in a dark corner. See? Your plants look ! Keep up the good work!

thank you for the warm welcome, woodnative and your thorough advice! I am excited to repot my Sans. I hope it can still wait til my succulent mix arrives. I will also cut off this infected leaf. Once cut will it grow back?

I've also noticed this lil sprout this morning. so thrilled that there might be hope for it. should I repot them together or separately?

My dream is to see it multiply and grow taller (although I'm not sure if this is a variety that does that) so I can have many of them for every corner.

I also enjoy checking the plants first thing in the morning. Looking at their leaves and touching their soil to feel if they need water. Also I try to watch out for bugs. Do you have any suggestions on how I can avoid them? My apartment is carpeted so just imagine the headache when something like that happens.

I really hope to get better at this coz it is truly such a delight to gaze at my mini window garden every morning as I sip a cuppa tea. But it seems though that my ordeal continues. One of my lavender isn't doing well :(

Woodnative's analysis was good enough. I just want to add that Sans is very drought tolerant. It's much better to be on the dry side than overwatering. Sans shouldn't be on the same watering schedule as your other plants. Personally I think watering once per week is way too much, unless the sans is very close to a heat source or under intense light. If you always have the curtain closed and the sans can't get direct sun, I'd say probably watering once or twice per month is enough in summer and spring.