Can one contribute to a RIRA and TIRA in the same year? (Splitting the $6000 contribution limit between the 2)
Yes
IRA Contribution Limits
Your total IRA contributions, whether you have one type of IRA or both, are capped at $6,000 for 2021. However, if you're age 50 or older, you're permitted an additional $1,000 in catch-up contributions, for a total of $7,000 for the year.
This contribution limit applies to all your IRAs combined, so if you have both a traditional IRA and a Roth IRA, your total contributions for all accounts combined can't total more than $6,000 (or $7,000 for those age 50 and up). You get to decide how to allocate the contribution, however. If you wanted to put $50 in a traditional IRA and the remaining $5,950 in a Roth IRA, you could. Or you could put the maximum amount in just one IRA.