This is what Ro (big thanks!) and I managed to cobble together. I will be updating this as time goes by, roughly once a week, but do let me know if anything is wrong / missing. At the end you have an overview of returning 2020 artists.

National Selection / National Final / Internal Selection / ESC events

January

11 January
NORWAY - first 10 NF acts revealed

13 January
FINLAND reveals NF acts

16 January
LITHUANIA First Heat
NORWAY Semifinal One

20 January
PORTUGAL reveals NF acts

23 January
LITHUANIA Second Heat
NORWAY Semifinal Two

25 January
ISRAEL National Final (Eden Alene, songs only)

30 January
FRANCE National Final
LITHUANIA Semifinal
NORWAY Semifinal Three

February
CZECH REPUBLIC reveals song (Benny Cristo)
SPAIN chooses songs (Blas Cantó)

6 February
LITHUANIA National Final
SWEDEN Semifinal One
NORWAY Semifinal Four

10 February
DENMARK reveals NF songs
SPAIN reveals two songs to be voted on (Blas Cantó)

13 February
CROATIA National Final
SWEDEN Semifinal Two
NORWAY Semifinal Five

15 February
NORWAY Wilcard Round

18 February
ESTONIA – Semifinal One

20 February
FINLAND National Final
NORWAY National Final
SWEDEN Semifinal Three
ESTONIA Semifinal Two
PORTUGAL Semifinal One

23 February
SAN MARINO revelas song (Senhit)

24 February
CYPRUS reveals song (Elena Tsagrinou, "El Diablo")

25 February
GERMANY reveals song (Jendrik)

27 February
SLOVENIA reveals song (Ana Soklič)
SWEDEN Semifinal Four
PORTUGAL Semifinal Two

March
AUSTRIA reveals song (Vincent Bueno)
AZERBAIJAN reveals song (Efendi)
BULGARIA reveals song (Victoria)
CYPRUS reveals song (Elena Tsagrinou, “El Diablo”)
GREECE reveals song (Stefania, “Last Dance")
IRELAND reveals song (Lesley Roy)
MOLDOVA reveals song (Natalia Gordienko)
SWITZERLAND reveals song (Gjon's Tears)
ESC Deadline for Song Submission

2 March
ITALY Sanremo First Night

3 March
ITALY Sanremo Second Night

4 March
ITALY Sanremo Third Night

5 March
ITALY Sanremo Fourth Night

6 March
ITALY National Final
PORTUGAL National Final
ESTONIA National Final
DENMARK National Final
SWEDEN Andra Chansen

12 March
LATVIA reveals song (Samanta Tīna)

13 March
SWEDEN National Final
ICELAND reveals song (Daði og Gagnamagnið)

26 March
ESC Deadline for backup performance recordings

Events
10 April - Eurovision In Concert 2021, Amsterdam (tbc)

23 countries retaining their 2020 artist:
AUSTRALIA - Montaigne
AUSTRIA - Vincent Bueno
AZERBAIJAN - Efendi
BELGIUM - Hooverphonic
BULGARIA - Victoria
CZECH REPUBLIC - Benny Cristo
GEORGIA - Tornike Kipiani
GREECE - Stefania
HOLLAND - Jeangu Macrooy
ICELAND - Daði og Gagnamagnið
ISRAEL - Eden Alene (+ songs national final)
IRELAND - Lesley Roy
LATVIA - Samanta Tīna
MALTA - Destiny
MOLDOVA - Natalia Gordienko
MACEDONIA - Vasil (Garvanliev)
ROMANIA - Roxen (+ songs national final)
SAN MARINO - Senhit
SERBIA - Hurricane (+ songs national final)
SLOVENIA - Ana Soklič
SPAIN - Blas Cantó
SWITZERLAND - Gjon's Tears
UKRAINE - Go-A

Plus
- 11 National Finals + 3 which are songs only (see above)
- 3 already / internally selected: ALBANIA, CYPRUS (song to be revealed), GERMANY (song to be revealed)
- 4 without any formal announcement: ARMENIA, POLAND, RUSSIA, UNITED KINGDOM.

Its all going to be cancelled

Thanks for the calendar, Boby!

...and Norman. Next year you can do it, three years in a row is enough for me.

I think you forgot the Estonian final.

It is already there on 6 March - it's not next Saturday, if that's what you thought.