adding 220v 50 amp circuit-breaker

Space marked 1 appears to have a label indicating you cannot use that space. That is common in panels that have stab limits, meaning the piece that opposing breakers clip onto can only handle the heat caused by up to a given limit. This limit would be found on the panel cover. It appears your bottom 100A and 20A may exceed stab limits too.

Space marked 2 is only a single pole, you would only get 120v from that space alone.

Your overall load is a concern, with a 100A in and a 100A out, but it seems like you aren't experiencing overload currrently, you may not if you add the hot tub. Likely the tub doesn't draw a full 50A.

Making space to accommodate a two-pole 50 can be made by substituting a breaker similar to a q25020c (upc 783643194984) in place of adjacent 20A breakers. I can't make a specific recommendation because you got tape gumming up critical information and you haven't provided.

But the biggest concern you got here is you appear to have breakers incompatible with the Listing of the panel. You haven't provided specific information, but I have never seen an electrical panel that is NRTL (UL, CSA ,ETL or similar) approved for use with Siemens, Challenger, and Eaton circuit breakers. You should check the information on the panel cover and arrange to get breakers replaced that are compatible.

Also I can see a couple of places that it appears a ground wire and neutral are terminated in a single lug hole. I have seen panels that the listing and labeling allows multiple grounds, but never one that allows multiple wires with a neutral termination.