You will not get definitive answers about the algorithm from Upwork's moderators or community members. Upwork does not offer a full view of its algorithm's functionality. However, based on my experience and my knowledge of ranking algorithms:
Proposal Submission and Visibility: How does the Upwork algorithm work when submitting a proposal? Is it crucial to send a proposal within the first five minutes to get the client's attention? For instance, if I submit my proposal within five minutes but the client doesn't open any proposals for the next ten minutes, and by then, the number of proposals reaches over 50, will my proposal end up on the last page? Additionally, if I send my proposal when there are already 20-50 proposals, will my proposal be pushed to the last page?
Some freelancers believe it is important to submit a proposal as soon as a job is posted. However, this approach does not always increase their chances of winning the job. Proposals are not ranked by time of receipt; rather, proposals are ranked according to job relevance, the freelancer's skills / experience, and other unknown factors.
With that, it really should not matter when your proposal is sent--this is why an algorithm is used. For example, if a client has received 49 proposals and you send your proposal (the 50th proposal received by the client), your proposal may or may not appear as the 50th proposal in the client's list. If your proposal (along with your profile and other factors considered) are a best-match, the algorithm should rank your proposal as Best Match and position it accordingly. This means, your proposal could end up in the 5th, 10th or 30th position among the 50 proposals the client sees.
The only occasion when time should matter is if the client has already started reviewing proposals via the website or email. If your proposal has yet to arrive, it will not appear in the client's list. If, however, the client posts a job and does not return for 5 days, the client will see the full list of 50 proposals, ranked in accordance with the algorithm. (For this argument, we are assuming the client received only 50 proposals. Proposal rankings change as more and more proposals arrive.)
Specialized Profiles and Searchability: Do specialized profiles help increase profile searchability and invite rates? For example, if a client uses a filter for the lead generation category, will profiles without a specialized lead generation profile be excluded from the search results? Also, is there any linkage between specialized profiles and search engine optimization within Upwork's platform?
This is a bit complicated because Upwork does not reveal exactly how its search mechanism works between main profiles and specialized profiles. According to Upwork, having a specialized profile can help increase a freelancer's searchability, but freelancers are not exactly sure how. If a profile does not appear when a client uses a category filter, it could be because there is no specialized profile. I have heard Upwork moderators say this as well.
As you might expect, the higher your profile appears in search results, the higher your chances of being seen, which could lead to more invites. This is no different than appearing low or high in Google or Bing search results. If you appear on page 1 of search results, you usually get more clicks than someone appearing on page 50..
Clients can search Upwork using keywords or pre-defined skill categories. The skill categories selected in a freelancers' profile (skills list) play a big role in searches. In your example, if you do not have a Lead Generation specialized profile, but include Lead Generation in your skills list, your profile should show up for lead generation. If you have a Lead Generation specialized profile and exclude Lead Generation from your skills list, the search results vary. I think searchability improves if you have Lead Generation in your skills list and have a Lead Generation specialized profile.
From what I can tell, Upwork's search function reviews the entire profile (title, summary, portfolio, skills, specialized profiles, etc.) for skill categories. However, simply filling a profile full of keywords ("keyword stuffing") does not help with searchability.
Also, I have seen no evidence that a specialized profile helps with SEO. Similar to what is stated above, a specialized profile seems to help with searchability (being found in search results) but not positioning (high or low in search results).
