At our table, we generally have "catch up karma". If a player loses their character, or you get a brand new player at the table, we build the character as per the standard build priority / method for the game or campaign at hand.
But, they then get a wodge of karma allocated to them, increasing their karma pool as appropriate. We normally give enough to get them to 1 less karma pool than the next weakest person at the table.
the idea is obviously to bring someone in with at least a few re-rolls available, and some improved skills so they are somewhat competitive, at least in a small specialist area. But, unlike character creation build points, they have to spend the karma as if they were raising the skills in game.

Does everyone else do this too?
Do you work on another way of bringing people up to a certain level of experience?
Do you make people start at the bottom of the ladder and play cautiously?

We do something similar: new players' characters get bonus karma equal to half the karma earnt by the most experienced active character at the table; old players' new characters get three quarters of the karma of their deceased / retired character.

One problem with calibrating new recruits from the weakest in the herd is turnover (most of my players are students). Someone who joins in week 1 is a step below last year's characters, but then someone joins in week 2 and they're a step below that and someone who joins in week 3 starts asking "if the person who joined in week 1 never comes back to play, can they all shuffle up one step?"

I don't have a standing rule for catching people up that are new to the game. In my experience, except for Extremely advanced games, brand new characters can usually keep up with a team that otherwise has a few runs under their belt.

On the other hand, though, I do believe in the idea that existing characters should continue to function. I keep track of an actual in-game calendar that keeps moving forward as the game progresses, so if someone misses a few weeks (in or out of game), there is a distinct possibility that their character might have trouble catching up on rent/etc. So I based my rule on the principle that a missing player's character is still doing something even if it isn't big important Shadowruns. I usually award 1 karma and 2,000 nuyen to the character for each week (in-game) that they were "busy keeping busy" and whatnot. If they wish, they can trade in either the karma or the nuyen to double the other (so, for example, they could get 2 karma and no money). This is a "your character survived this week" sort of award.

I only use that rule when the absence is reasonable, and usually it only ends up getting used when I get someone else to GM for a bit (the GM's character still gets some advancement, even though they aren't active). If a player is gone for an extended period without cause, I'll usually just hand-wave their lifestyle for the time and jump in without any extra bonus...

Thats Standard in a lot of German Rounds .
I'm playing RPG for nearly 35 Years now and this has always been our default Rules (no matter which Group , which RPG . As far as I remember)
Most often we give a New Player enough XP / Karma to the average of the other Chars or at least up to the least experienced Char .

New Chars are still ...."at a disadcvantage" because they didn't get the Connections or better equipment that played chars receive ingame

with an average Dance
Medicineman

That's what I generally go with as well - the advantage to having made contacts and worked out who has "friends of friends" that can get you stuff, and either the loot from previous runs, or the time spent getting high availability items really makes the difference between two otherwise equal characters.

I'll add to the chorus, yeah I give new PCs a starting krma boost to "catch them up" probably not 100% of what the established characters had, buut some wherein the 2 thirds to 75% region.

We only allow gaining nuyen in downtime if the character has the Day Job flaw, Instruction skill, or some other mechanical way of earning their rent. Without it, characters who don't keep up maintenance on lifestyle, contacts and SotA, find those things degrade from neglect.

Well, that implementation isn't meant as a way for characters to earn money without trying. It is meant as a means to help bridge the gap between "you weren't here, so your character was just sitting in his doss picking his nose for the last 3 weeks" and "you probably did something to make ends meet while the rest of the team did that run (or two)"

I primarily use it for when somebody steps in to GM for a bit, their character still earns a bit of cash and karma without them needing to worry about it.

And really, just because a player can't make it to play, does that mean that their character should suddenly be evicted because they couldn't earn any cash, I think it makes more sense that they would be doing something to make ends meet.

For our group, when creating missions, I like to assign Karma per objective, usually 3-5 karma for the primary objective and 1-2 karma for secondary objectives. Any new character created in the same "campaign" starts with Total Karma equal to all of the primary karma earned by the group, with an additional 500-1000 nuyen (post char-gen) per primary karma. It lets the group try out different characters, doesn't hurt someone too badly if their character dies, but still gives the players an incentive to stick with their current characters.

Mostly we have a fairly stable group and only play when all can play, so mostly this doesn't come into play.
However, we had a couple of times a game (shadowrun, alternity,...) which we would play when not everybody could join. I once GM'ed that one and what I would do was to boost characters up when they dropped behind. I kept a sheet with all the karma the other players had gained and I would put them a bit below the others. Since it was (except for a one or two players who almost always joined in) different players who didn't join in, it was only sometimes needed (if player A didn't join in week 1 and player B wouldn't join in week 2, they would be close enough that it didn't matter).

I would encourage the player to come up with something for their character to do during that time (like work with a contact or something like that).