There is no base R "year-week" type but if you can work with character or numeric type data, then this should work
format(seq(from = as.Date("2019-01-01"), to = as.Date("2020-12-31"), by = "week"), "%Y%V")
#> [1] "201901" "201902" "201903" "201904" "201905" "201906" "201907" "201908"
#> [9] "201909" "201910" "201911" "201912" "201913" "201914" "201915" "201916"
#> [17] "201917" "201918" "201919" "201920" "201921" "201922" "201923" "201924"
#> [25] "201925" "201926" "201927" "201928" "201929" "201930" "201931" "201932"
#> [33] "201933" "201934" "201935" "201936" "201937" "201938" "201939" "201940"
#> [41] "201941" "201942" "201943" "201944" "201945" "201946" "201947" "201948"
#> [49] "201949" "201950" "201951" "201952" "201901" "202002" "202003" "202004"
#> [57] "202005" "202006" "202007" "202008" "202009" "202010" "202011" "202012"
#> [65] "202013" "202014" "202015" "202016" "202017" "202018" "202019" "202020"
#> [73] "202021" "202022" "202023" "202024" "202025" "202026" "202027" "202028"
#> [81] "202029" "202030" "202031" "202032" "202033" "202034" "202035" "202036"
#> [89] "202037" "202038" "202039" "202040" "202041" "202042" "202043" "202044"
#> [97] "202045" "202046" "202047" "202048" "202049" "202050" "202051" "202052"
#> [105] "202053"
Created on 2022-02-24 by the reprex package (v2.0.1)