The most significant immediate Biden Administration immigration and international travel related actions

Great question. Holland & Knight in a web publication dated January 26, 2021, summarized them as stated below.
1. Required to produce proof of a recent negative COVID-19 test before entry; and
2. Required to comply with other applicable CDC guidelines concerning international travel, including recommended periods of self-quarantine or self-isolation after entry into the United States.
3. Revoked the Muslim and African travel bans 4.0 and 3.0 affecting citizens of Iran, Libya, Somalia, Syria, Yemen, Venezuela, North Korea, Belarus, Burma, Eritrea, Kyrgyzstan, Nigeria, Sudan, and Tanzania. The Department of State through its authorized local U.S. embassy or consulates can immediately process visa applications for individuals from the affected countries on a post-by-post basis, consistent with the Department’s ongoing COVID-19 pandemic-related guidance for safely returning our workforce to Department facilities.
4. 100-day pause on deportations and rescission of the February 2017 Trump order announcing all-out enforcement without any prioritization.
5. Declaration of the end of the “national emergency” at the southern border
6. Preservation of and Plans to Strengthen the DACA Initiative
7. Suspensions of New Enrollments in Migrant Protection Protocols Program
8. Extension of Deferred Enforcement Departure for Liberians for 18 Months
9. Halt of President Trump’s plan to exclude non-citizens from the census and apportionment of congressional representatives.
10. Review of any pending regulatory actions for possible withdrawal and delay of effective dates of regulations that were published but have not yet taken effect.

As reported by AILA’s Jan 22, 2021 post, President Biden has also sent an immigration bill to Congress for Senator Robert Menendez (D-NJ) and Congresswoman Linda Sánchez (D-CA) to sponsor. Here are the key provisions of the proposed bill:
1. Legalization and path to citizenship for unauthorized immigrants
2. Reforms to the family-based immigration system, including:
3. Reforms to the employment-based immigration system, including:
4. Diversity Visa Program will be increased to 80,000 visas per year (from 55,000)
5. Reforms to the immigration courts, including steps to reduce backlogs and restoration of judicial discretion to grant relief
6. Expansion of legal representation and legal orientation programs
7. Improvements to asylum, U visa, T visa, and VAWA humanitarian programs, including the elimination of the 1-year asylum filing deadline and increase of the U visa cap to 30,000 visas
8. Prohibition against future discriminatory bans such as the Muslim and African travel bans
9. Reforms to manage the border and ports of entry including increased accountability measures and increased resources, technology, and infrastructure
10. Programs and funding to address the root causes of migration from Central America
11. Protection for workers from exploitation